生物化学英文版练习题及答案。。。。精_生化练习题含答案

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Gloary for Biochemistry

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acetyl CoA carboxylase An enzyme that catalyzes the ATP-dependent synthesis of malonyl CoA from acetyl CoA and carbon dioxide, the committed step in fatty acid synthesis.acetylcholine A common neurotransmitter that exerts its effects by first binding to the acetylcholine receptor.acetylcholine receptor A ligand-gated channel that promotes a large inward current of sodium ions and triggers an action potential;composed of a pentamer of four kinds of polypeptide subunits, the channel opens to allow paage of sodium and potaium ions when two acetylcholine molecules promote transient opening of the channel.activated carriers Small molecules carrying activated functional groups that can be donated to other molecules;for instance, ATP carries activated phosphate groups and CoA carries activated acyl groups.activation domain The structural region of a transcription factor that facilitates transcription in some manner.See also DNA-binding domain.active site A specific region of an enzyme that binds the substrate and carries out catalysis.active transport The transport of an ion or a molecule against a concentration gradient, where DG for the transported species is positive;the proce must be coupled to an input of free energy from a source such as ATP, an electrochemical gradient of Na+ or K+, or light.acyl adenylate A mixed anhydride in which the carboxyl group of a molecule is linked to the phosphoryl group of AMP;the formation of acyl adenylates is a means of activating carboxyl groups in biochemical reactions, such as the formation of fatty acyl CoA molecules from a free fatty acid and coenzyme A.acyl carrier protein(ACP)A bacterial polypeptide that is linked to phosphopantetheine and acts as a carrier of the growing fatty acyl chain during fatty acid biosynthesis.addition to or formation of double bond A reaction in which a functional group is added to a double bond or a group is removed from a molecule to form a double bond.adenylate cyclase An enzyme that generates cAMP, a second meenger, from ATP.adipocytes Mammalian cells that are the major storage site for triacylglycerols.aerobic glycolysis The use of lactic acid fermentation to generate ATP even the presence of enough oxygen to support cellular respiration.aerobic In the presence of oxygen.affinity chromatography A protein-purification technique based on the high affinity of many proteins for specific chemical groups.Such groups are attached to an inert matrix, and the protein sample is applied;only those proteins with an affinity for the groups will bind.affinity labeling A means of mapping the active site of an enzyme by using a substrate analog that binds to the active site and forms a covalent bond with a nearby amino acid.agonists Molecules that bind to receptor proteins and trigger signaling pathways.alcoholic fermentation The anaerobic conversion of glucose into ethanol with the concomitant production of ATP.aldolase An enzyme that cleaves an aldol.Aldolases are important in carbohydrate metabolism.aldose A monosaccharide whose C-1 carbon atom contains an aldehyde group.allosteric interaction An interaction between a small molecule(a ligand)and a site on a protein that may be some distance away from the active site;the interaction causes a conformational change and consequent alteration in the catalytic activity of the protein.α helix A common structural motif in proteins, in which a polypeptide main chain forms the inner part of a right-handed helix, with the side chains extending outward;the helix is stabilized by intrachain hydrogen bonds between NH and CO groups of the main chain.α-ketoglutarate dehydrogenase A citric acid cycle enzyme that catalyzes the oxidative decarboxylation of α-ketoglutarate to yield succinyl CoA.This enzyme, which helps to regulate the rate of the citric acid cycle, is structurally and mechanistically similar to the pyruvate dehydrogenase complex.α-amylase A hydrolytic enzyme that cleaves the a-1,4 bonds of starch and glycogen, but not the a-1,6 bonds.Ames test A simple, rapid means of detecting carcinogens by measuring a chemical's ability to induce mutations in Salmonella bacteria.amiloride-sensitive sodium channel A sodium channel important in the detection of the taste of salt.Such channels are inhibited by amiloride, which also mutes the taste of salt.amino acid An organic acid with an α-carbon atom linked to a carboxylic acid, an amino group, a hydrogen atom, and a side chain(the R group).Twenty different amino acids are the building blocks of proteins.amino sugar A sugar that contains an amino group rather than a hydroxyl group at the C-2 position;the most common amino sugars are glucosamine and galactosamine.aminoacyl-tRNA An amino acid ester of transfer RNA.aminoacyl-tRNA synthetase An enzyme that activates an amino acid and then links it to transfer RNA.Also known as an activating enzyme, each aminoacyl-tRNA synthetase is specific for a particular amino acid.aminotransferase(transaminase)A cla of enzymes that transfer an α-amino group from an α-amino acid to an α-keto acid.Also called transaminases.ampere A measure of electrical current: the flow of 6.24 × 1018 charges per second.amphipathic molecule A molecule, such as a membrane lipid, that contains both a hydrophobic and a hydrophilic moiety.amylopectin The branched form of starch, containing glucose residues in about one α-1,6 linkage per thirty α-1,4 linkages.amylose The unbranched form of starch, containing glucose residues in α-1,4 linkage.anabolism The set of metabolic reactions that require energy to syntheize molecules from simpler precursors.anaerobic In the absence of oxygen.anaplerotic reaction From the Greek for “fill up,” referring to a reaction that replenishes intermediates removed from a metabolic pathway.The most common example is the reaction catalyzed by pyruvate carboxylase, in which the carboxylation of pyruvate produces oxaloacetate, a key component of the citric acid cycle.anion exchange Ion-exchange chromatography in which a protein mixture is paed through a column containing a matrix bearing positive charges.Proteins bearing negative charges will bind to the column while those with positive charges will pa through the column.anomers Isomers of cyclic hemiacetals or hemiketals, with different configurations only at the carbonyl carbon atom;that carbon is known as the anomeric carbon.antagonist A molecule that binds to a receptor protein but does not trigger the signaling pathway.Such molecules are like competitive inhibitors for enzymes.antibody A protein synthesized by an animal in response to the presence of a foreign substance, or antigen;often binds to the antigen, neutralizing it or marking it for destruction.anticodon Three-nucleotide sequence of tRNA that base-pairs with a codon in mRNA.antigen A foreign substance that elicits the synthesis of an antibody.antigenic determinant Site on an antigen to which an antibody binds.Also called an epitope.antigenic determinant The specific site on an antigen that is recognized by an antibody.Also known as an epitope.antimycin A An antibiotic from Streptomyces that inhibits the respiratory chain by blocking electron transfer in the cytochrome reductase complex.antiserum Serum prepared from the blood of an immunized animal containing soluble antibodies specific for a particular antigen.apoptosis A cascade of proteolytic enzymes that results in controlled cell death in response to significant cell damage or specific developmental programs.Also called programmed cell death.Archaea The domain of life that comprises single cell organisms lacking a nucleus.Formerly believed to be member of the domain Bacteria, Archaea are now known to have a unique evolutionary history with biochemical characteristics different from the other two domains of life.ascorbate(vitamin C)A water-soluble vitamin that functions as an antioxidant and is required for the hydroxylation of collagen;scurvy results if ascorbate is deficient.aay A test for some unique identifying property of a protein to be purified.ATP(adenosine 5'-triphosphate)A nucleotide consisting of adenine, ribose, and triphosphate units that serves as the cellular energy currency.ATP synthase Molecular aembly of the inner mitochondrial membrane responsible for the respiratory-chain-driven synthesis of ATP.Also called Complex V, mitochondrial ATPase, H+-ATPase, or F0F1-ATPase.ATPase Enzymes that catalyze the hydrolysis of adenosine triphosphate(ATP)to form adenosine diphosphate(ADP)and inorganic phosphate(Pi)and use the energy released to power otherwise endergonic reactions.ATP-driven pump Membrane proteins that use the energy of ATP hydrolysis to drive the thermodynamically uphill transport of ions or molecules.autoradiography A means of detecting radioactive molecules immobilized in a separation medium such as polyacrylamide;the radioactivity of the molecules will blacken x-ray film.B

Bacteria The domain of life that comprises single cell organisms lacking a nucleus.Members of this domain differ evolutionarily and biochemically from the Archaea, with whom they were formerly grouped.bacterial artificial chromosome An artificial bacterial chromosome, a highly engineered version of the E.coli fertility(F factor), that can serve as a cloning vector for inserts as larges as 300 kb.bacteriorhodopsin A 26-kd integral membrane protein that absorbs light and converts its energy into proton-motive force, which is then used to synthesize ATP.ball-and-chain model A model for the regulation of the K channel that postulates that the first +20 residues of the K channel form a cytoplasmic unit(the ball)that is attached to a flexible segment of the polypeptide(the chain).When the channel is closed, the ball rotates freely in the aqueous solution.When the channel opens, the ball quickly finds a complementary site in the open pore and occludes it.basic-leucine zipper(bZip)protein A eukaryotic DNA binding unit that consists of a pair of long  helices.Because these pairs are often stabilized by appropriately spaced leucine residues, these structures are often referred to as leucine zippers.B-DNA helix A right-handed double helix with the following characteristics: the two strands are antiparallel;the bases are inside the helix and the phosphates and deoxyribose sugars are on the outside;adenine forms hydrogen bonds with thymine, and guanine forms them with cytosine;the bases in each pair are coplanar;there are 10.4 residues per turn, with a pitch of 35 Å.β sheet A common structural motif in proteins, in which two or more β strands are aociated as stacks of chains, stabilized by interchain hydrogen bonds;a number of β strands running in the same direction form a β pleated sheet, whereas such strands running in opposite directions form an antiparallel pleated sheet.β-galactosidase An eential enzyme in lactose metabolism that hydrolyzes lactose into galactose and glucose.bifunctional enzyme An enzyme with two different, often opposing, catalytic activities on one polypeptide chain.For instance, phosphofructokinase 2 synthesizes fructose 2,6-bisphosphate and fructose 2,6-bisphosphatase hydrolyzes it, yet both active sites are on the same polypeptide chain.bile salts Polar derivatives of cholesterol that are made in the liver, stored in the gall bladder, and released into the small intestine, where they act as detergents to solubilize dietary lipids, facilitating their digestion and absorption.biological macromolecule

Large molecules such as proteins and nucleic acids, that are key functional and structural components of living systems.biotin A vitamin that plays a role in carboxylation and decarboxylation reactions.2,3-bisphosphoglycerate An allosteric effector of hemoglobin that decreases the affinity of hemoglobin for oxygen.blood–brain barrier The tight junctions between endothelial cells that line blood veels within the brain and spinal cord.body ma index(BMI)A value, calculated by dividing a person’s weight in pounds(kg)by 2(height in inches(cm)), that is a reliable indicator of obesity for most people.Bohr effect The observation made by Christian Bohr that H+ and CO2 promote the release of oxygen from oxyhemoglobin.bongkrekic acid An antibiotic that inhibits the action of ATP-ADP translocase.buffer An aqueous solution consisting of a weak acid and it conjugate base(or vice versa)that resists changes in pH when strong acids or bases are added.+

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C3 plant A plants that lacks the C4 pathway.C4 pathway A means by which four-carbon compounds, such as oxaloacetate and malate, carry carbon dioxide from mesophyll cells in contact with the air to bundle-sheath cells, which are the 4 major sites of photosynthesis.The pathway accelerates photosynthesis by concentrating carbon dioxide in photosynthetic cells.C4 plant A plant that utilizes the C4 pathway.CAAT box A component of many eukaryotic promoters with the consensus sequence 5'-GNCAATCT-3'.calorie The amount of heat required to raise the temperature of 1 gram of water from 14.5°C to 15.5°C.Calvin cycle(Dark reactions)In plants, a cyclic metabolic pathway in which carbon dioxide is incorporated into ribulose 1,5-bisphosphate to give compounds that can be used for the synthesis of glucose.5' cap A structure at the 5' end of eukaryotic mRNA that stabilizes the mRNA and enhances its translation.The cap contains a 7-methyl guanylate residue attached by a triphosphate linkage to the sugar at the 5' end of the mRNA in a rare 5'-5' linkage.carbohydrates Saccharides, which are aldehyde or ketone compounds with multiple hydroxyl groups.Also defined as organic compounds with the empirical formula(CH2O)n.carbon monoxide CO;A colorle, odorle gas that binds to hemoglobin at the same site as oxygen and thereby prevents oxygen binding.carbonic anhydrase An enzyme that catalyzes the reaction of carbon dioxide with water to form carbonic acid.carbonium ion A carbon compound that contains a positively charged carbon atom;a carbonium atom is critical for catalysis by lysozyme

carboxyhemoglobin A complex of carbon monoxide and hemoglobin that does not bind oxygen.carboxylase An enzyme that catalyzes a carboxyl transfer reaction;biotin is usually required as a coenzyme.carnitine A zwitterionic compound formed from lysine that acts as a carrier of long-chain fatty acids from the cytosol to the mitochondrial matrix.cascade, enzymatic A sequence of reactions, in which at each step a product stimulates an ensuing reaction, generating an amplification of a relatively small stimulus or signal.catabolism The set of metabolic reactions that transform fuels into cellular energy.catabolite activator protein(CAP)The cAMP response protein;when bound to cAMP, CAP binds to an inverted repeated of the lac operon, near position-61 relative to the start site of transcription, to stimulate transcription.catabolite repreion The repreion by glucose of catabolic enzymes required for the catabolism of carbohydrates other than glucose.catalase A ubiquitous heme protein that catalyzes the dismutation of hydrogen peroxide into molecular oxygen and water.catalysis by approximation Enhancing the rate of a reaction by bringing multiple substrates together along a single binding surface of an enzyme.catalytic antibodies Antibodies generated by using transition-state analogs of a particular reaction as antigens.Such antibodies often function as catalysts for the reaction.Also called abzymes.catalytic group An amino acid or cofactor at an enzymes active site that directly participates in the making or breaking of covalent bonds.catalytic RNA One of a cla of RNA molecules that display enzymatic activity.catalytic triad A constellation of three residues, found in many proteolytic enzymes, in which two of the residues convert the remaining residue, usually a serine or cysteine, into a potent nucleophile.cation exchange Ion-exchange chromatography in which a protein mixture is paed through a column containing a matrix bearing negative charges.Proteins bearing positive charges will bind to the column while those with negative charges will pa through the column.CD4 A protein present on the surface of helper T cells that, along with the T-cell receptor, binds to cla II MHC proteins on antigen-presenting cells.CD4 is the source of the specificity of helper T cells for cla II MHC interactions.cDNA library A collection of all of the complementary DNA for all mRNA that a cell contains, which have been inserted into vectors, and then inserted into bacteria.CDP-alcohol Activated form of an alcohol that can be used in the synthesis of phosphoglycerides by combining with diacylglycerol at the free hydroxyl group on glycerol;for instance, CDP-choline can react with diacylglycerol to form the phospholipid phosphatidylcholine.CDP-diacylglycerol(cytidine diphosphodiacylglycerol)Formed from phosphatidate and cytidine triphosphate(CTP);activated diacylglycerol used in the synthesis of phosphoglycerides such as phosphatidyl serine.cell cycle The coordination of DNA replication and cell division in eukaryotes.Mitosis takes place only after DNA synthesis.Two gaps(G1 and G2)in time separate the two procees.cellular respiration The generation of high-transfer-potential electrons by the citric acid cycle, their flow through the respiratory chain to O2, and the accompanying synthesis of ATP.cellulose An unbranched homopolysaccharide in plants, composed of glucose residues in α-1,4 linkage;the major structural polysaccharide in plants.ceramide(N-acyl sphingosine)A sphingosine with a long-chain acyl group attached to the amino group.cerebroside A sphingolipid in which glucose or galactose is linked to the terminal hydroxyl group of a ceramide.cGMP phosphodiesterase An enzyme that hydrolyzes cyclic GMP to GMP;in the visual system, this hydrolysis leads to the generation of an action potential. chain One of the protein subunits of hemoglobin.Hemoglobin is composed of two  chains and two  chains. chain One of the protein subunits of hemoglobin.Hemoglobin is composed of two  chains and two  chains.channel A protein paage that is continuous and that allows ions to flow rapidly through a eukaryotic membrane from a compartment of higher to a compartment of lower concentration.Channels(also known as pores in bacteria)are generally composed of four to six subunits, or domains, and are gated by membrane potential, allosteric effectors, or covalent modification.channel Membrane proteins that provide a pore through which ions can flow very rapidly in a thermodynamically downhill direction.chaperone proteins Slow ATPases that bind newly synthesized proteins and aist their proper folding.chemical modification reaction A reaction in which a molecule modifies a specific amino acid residue in a protein.chemiosmotic hypothesis The idea that electron transfer in the respiratory chain is used to pump protons acro the inner mitochondrial membrane, establishing a proton gradient;this gradient(the proton-motive force)drives the synthesis of ATP by ATP synthase.chitin A glycosaminoglycan found in the exoskeleton of insects, crustaceans, and arachnids and is, next to cellulose, the second most abundant polysaccharide in nature.chloroplast The plant organelle in which photosynthesis takes place.cholesterol A sterol that is an important constituent of eukaryotic membranes as well as lipoproteins;also a precursor of steroid hormones.chromatin immunoprecipitation(ChIP)A technique for identifying the binding sites of DNAbinding proteins.The protein is cro-linked to DNA to which it is bound in chromatin, and the DNA is fragmented into small pieces.Antibodies to the bound protein are used to isolate the chromatin fragments with the bound protein.The cro-linking is reversed, and the DNA is isolated and characterized.chromatin Nucleoprotein chromosomal material consisting mainly of DNA and histones.chylomicrons Lipoprotein particles that transport dietary triacylglycerols from the intestine to other tiues;apolipoprotein B-48 is a protein component of chylomicrons.citrate synthase An enzyme that catalyzes the condensation of acetyl CoA with oxaloacetate to form citrate, initiating the citric acid cycle.citric acid cycle A cyclic series of metabolic reactions that completely oxidize acetyl units to carbon dioxide.Also known as the tricarboxylic acid cycle(after citrate)or the Krebs cycle, after Hans Krebs, who elucidated the cyclic nature of the pathway.coactivator Proteins that activate transcription by binding to specific transcription factors and then catalytically modifying chromatin components.cobalamin(vitamin B12)A complex taking part in a number of reactions including the formation of deoxyribonucleosides from ribonucleosides.coding strand The strand of DNA that has the same sequence as the RNA transcript except it contains thymine(T)in place of uracil(U).codon Nucleotide triplet in mRNA that encodes for a particular amino acid.coenzyme A(CoA)A coenzyme consisting of an adenine nucleotide linked to pantothenate, which is itself linked to mercaptoethylamine;universal carrier of acyl groups, which are bound to the mercaptoethylamine unit.coenzyme A small organic molecule required for the activity of many enzymes;vitamins are often components of coenzymes.coenzyme Q A mobile electron carrier that is a component of the respiratory chain;it shuttles between the oxidized ubiquinone form to the reduced ubiquinol form through a semiquinone intermediate;accepts electrons from NADH-Q reductase as well as succinate-Q reductase.cofactors Small molecules, such as metals or coenzymes, that many enzymes require for catalytic activity.cohesive ends In double-stranded DNA molecules, complementary single-stranded ends produced by staggered cuts.Specific cohesive ends in DNA can be produced by certain restriction enzymes, such as EcoRI, and can then be used to join unrelated DNA molecules by annealing and joining with DNA ligase.collagen The main fibrous protein component of skin, bone, tendon, cartilage, and teeth;the collagen helix contains three helical polypeptide chains, each nearly 1000 residues long.Glycine appears at every third residue in the amino acid sequence, and the sequence glycine-proline-hydroxyproline recurs frequently.committed step The first irreversible step in a metabolic pathway under physiologic conditions;this step is catalyzed by an allosteric enzyme and commits the product to a particular chemical fate.competitive inhibition The reduction in the rate of enzyme activity observed when the enzyme can bind the substrate or the inhibitor but not both.Many competitive inhibitors resemble the substrate and compete with it for binding to the active site.Relief from inhibition by saturation with substrate is a kinetic hallmark of competitive inhibition.complementary DNA(cDNA)DNA complementary to an mRNA sequence.concerted mechanism A model explaining the kinetics of allosteric enzymes in which the transitions of all of the active sites between the T state and the R state occur simultaneously.consensus sequence Idealized base sequence that represents common features of a promoter site.conservative substitutions Mutations that replace one amino acid with another similar in size and chemical properties.constitutive genes Genes that are not subject to regulation and are constantly transcribed.convergent evolution The acquisition of similar structure to perform a similar biochemical activity in proteins that have evolved independently.convergent evolution The proce by which different evolutionary pathways arrive at the same solution to a biochemical problem.cooperative A property of allosteric proteins wherein the reactions at different sites are not independent of one another.cooperativity A property of many allosteric enzymes in which the binding of substrate to one active site favors the transition of all active sites from the T state to the R state, leading to an increase in enzyme activity.core glycosylation The addition of carbohydrates to proteins and the proceing of these carbohydrates that takes place in the endoplasmic reticulum.corepreor A small molecule that binds to a repreor protein;the corepreor-repreor complex then binds to the operator DNA of a particular operon to inhibit transcription.Cori cycle A cyclic metabolic pathway in which lactate from active muscle is converted into glucose by the liver, which in turn supplies newly synthesized glucose to muscle and other tiues.Cori disease A disease in which the structure of liver and muscle glycogen is abnormal and the amount is increased;it is due to an inability to hydrolyze the α-1,6-glycosidic bonds in glycogen;liver function is compromised.cotransporter Transporters that couple the thermodynamically unfavorable flow of one species of ion or molecule up a concentration gradient to the favorable flow of a different species down a concentration gradient.covalent bond A chemical bond formed by the sharing of pairs of electrons between adjacent atoms.Covalent bonds are the strongest chemical bonds.covalent catalysis Catalysis in which the active site contains a reactive group that becomes temporarily covalently modified in the course of catalysis.covalent intermediate In a catalytic mechanism, an intermediate comprising a component of the substrate covalently bound to the enzyme.covalent modification The attachment to and removal of chemical groups from an enzyme and the consequent change in the catalytic properties of that enzyme.Catalytic properties of many enzymes are altered by the covalent attachment and removal of phosphoryl groups, whereas a smaller number of others undergo reversible attachment of AMP units from ATP.CpG islands Regions of DNA rich in the sequence CpG, usually located at the 5' region of genes;the cytosine bases of these islands can be methylated to inhibit transcription of the aociated gene.creatine phosphate(phosphocreatine)In muscle, a compound with a high phosphoryl transfer potential that is used to regenerate ATP from ADP during the initial seconds of muscle contraction.cro talk Interactions between several signaling pathways.Cro talk permits more finely tuned regulation of cell activity than would the action of individual independent pathways.cyclic AMP(cyclic 3', 5'-adenosine monophosphate)A cyclic nucleotide formed from ATP and an important second meenger in a variety of signaling systems.cyclic GMP(cyclic 3', 5'-guanosine monophosphate)A cyclic nucleotide formed from GTP and an important second meenger in vision.cytochrome An electron-transferring protein that contains a heme prosthetic group whose iron component shuttles between the ferrous(+2)and ferric(+3)state during electron transfer.cytochrome c A water-soluble, highly conserved cytochrome component of the respiratory chain that accepts electrons from cytochrome reductase and is in turn oxidized by cytochrome oxidase.cytochrome c oxidase The final complex of the respiratory chain, cytochrome c oxidase transfers electrons from cytochrome c to molecular oxygen and concomitantly pumps protons acro the inner mitochondrial membrane to generate the proton-motive force.Also called Complex IV.cytochrome P450 monooxygenase A family of mixed function oxygenases that add OH groups to various biochemicals, including steroid hormones.These enzymes require NADPH, O2 and cytochrome P450.cytochrome P450 system Found in adrenal mitochondria and liver microsomes, an electron-transport chain in which the terminal component is cytochrome P450;this system plays a role in the detoxification of foreign substances by altering them to increase their solubility and facilitate excretion.cytoskeleton Internal scaffolding of cells, made up of microfilaments, intermediate filaments, and microtubules, which enables cells to transport vesicles, change shape, and migrate.D

dalton A unit of ma very nearly equal to that of a hydrogen ion and precisely equal to 1.000 on the atomic ma scale.dark reactions In chloroplasts, the reactions in which carbon dioxide is fixed into organic compounds, driven by ATP and NADPH.de novo pathway A biosynthetic pathway that builds the final product from simple precursors.See also salvage pathway.decarboxylase An enzyme that removes a carbon atom from a substrate in the form of carbon dioxide.denaturation A disruption in the native conformation of a macromolecule that causes a lo of normal function.deoxyhemoglobin A conformation of hemoglobin that is unable to bind oxygen.Also called the T or tense form.deoxynucleotide A nucleotide containing a purine or pyrimidine base covalently linked to 2-deoxyribose, which is in turn linked to one or more phosphate groups.deoxyribose A five-carbon monosaccharide(C5H9O5)that constitutes the carbohydrate moiety of a deoxynucleotide;the deoxyribose commonly found in deoxynucleotides is 2-deoxyribose.diabetes A disease characterized by the overproduction of glucose by the liver and its underutilization by other organs.Type I diabetes is due to an insufficiency of insulin production, whereas type II is due to the inability of insulin receptors to respond to the hormone.diacylglycerol A second meenger in the phosphoinositide cascade, which leads to the activation of protein kinase C.dialysis The proce of removing small molecules from a solution containing a mixture of large molecules and small molecules.The mixture is placed in a bag made of a semipermeable membrane, which is then placed in a different solution.The membrane allows escape by the small molecules but not the large molecules.diastereoisomers A pair of molecules, each with more than one asymmetric center, that have opposite configurations at one such center but are not mirror images of each other;in the aldotetrose series, Derythrose and D-threose are diastereoisomers. dimer A pair of subunits(11and22 that comprise the functional unit of hemoglobin.dimerization arm A molecular structure on the EGF receptor that is exposed only upon binding EGF and that subsequently reaches out and inserts into a binding pocket on another EGF receptor monomer, facilitating dimerization.direct repair A means of repairing damaged DNA in which the damaged region is corrected in place.For example, pyrimidine dimers are simply cleaved to restore the original nucleotides.dismutase An enzyme that catalyzes a dismutation reaction in which a single reactant is converted into two different products.diociation constant(Kd)A measure of strength of the interaction of a ligand for a receptor defined by the expreion Kd = [R] [L]/[RL] where [R] is the concentration of the free receptor, [L] is the concentration of the free ligand, and [RL] is the concentration of the receptor–ligand complex.distal histidine A histidine in globins that forms a hydrogen bond to the bound oxygen that helps to prevent the release of superoxide anion.disulfide bond A covalent bond formed by the oxidation of two sulfhydryl groups;the oxidation of cysteine residues in a polypeptide yields a disulfide bond linking the two residues.divergent evolution The evolutionary proce by which proteins with different properties are derived from a common ancestor.DNA ligase An enzyme that catalyzes the formation of a phosphodiester bond between the 3'-OH group at the end of one DNA chain and the 5'-phosphate group at the end of the other chain;it takes part in the synthesis, repair, and splicing of DNA.DNA microarray(gene chip)A solid support such as a microscope slide to which are affixed oligonucleotides or cDNAs corresponding to specific genes.Fluorescently labeled cDNA is hybridized to the slide to reveal the expreion level for each gene, identifiable by its known position within the microarray.DNA polymerases Enzymes that catalyze the template-directed, primer-dependent addition of deoxynucleotide units, using deoxynucleotide triphosphates as substrates, to the 3' end of a DNA chain;chain growth is in the 5'-to 3'-direction;such enzymes replicate and repair DNA.DNA probe A radioactively labeled, single-stranded specific base sequence used to locate a complementary sequence among DNA fragments displayed on an electrophoretic gel.DNA-binding domain The structural region of a transcription factor that recognizes and binds to a particular DNA sequence.See also activation domain.dolichol phosphate A lipid, residing in the ER membrane, containing approximately 20 isoprene units that serves as a carrier of oligosaccharides destined to be attached to a protein.domain An independently folded unit in the tertiary structure of a polypeptide chain;may contain a number of supersecondary structures.In multienzyme complexes, each domain may carry out one or more catalytic reactions.In proteins, a compact globular unit of 100 to 400 residues, poibly joined to other domains by a flexible polypeptide segment;often encoded by a specific exon in the gene encoding the protein.E

Edman degradation The sequential removal of the N-terminal amino acid from a protein as a phenylthiohydantoin derivative;used in sequencing proteins.EGF receptor(EFGR)A receptor tyrosine kinase that is activated by epidermal growth factor.The unbound receptor exists as a monomer, but dimerizes upon growth factor binding.eicosanoid A carbon compound containing 20 carbon atoms;prostaglandins are examples.Eicosanoids often act as local hormones.electrochemical potential(membrane potential)A thermodynamic measure of the energy resulting from an unequal distribution of a population of molecules acro a membrane that takes in account concentration differences and charge differences between the two sides of the membrane.electrophoresis A technique used to separate charged molecules, such as proteins and nucleic acids, that is based on the fact that such molecules will move at differing rates in an electric field, depending on factors such as net charge, size, and shape of the molecules.electrostatic interaction A bond formed when a charged group on one molecule attracts an oppositely charged group on another molecule.Embden-Meyerhof pathway Glycolysis.enantiomers A pair of molecules, each with one or more chiral centers, that are mirror images of each other.endoplasmic reticulum(ER)An extensive system of cytoplasmic membranes that comprises about half the total cell membrane.The region of the ER that binds ribosomes is called the rough ER, and the region that is devoid of ribosomes is called the smooth ER.enhancers DNA sequences that have no promoter activity themselves but that can greatly enhance the activity of other promoters;enhancers can exert their stimulatory effect over a distance of several thousand nucleotides.entropy A measure of the degree of randomne or disorder in a system;denoted by the symbol S in thermodynamics, the change in entropy(.S)increases when a system becomes more disordered and decreases when the system becomes more ordered, or le random.enzyme multiplicity A regulatory strategy in which the committed step common to several pathways is catalyzed by different enzymes with the same catalytic properties but different regulatory properties.Each enzyme thus responds to the final product of one of the pathways having the committed step in common.enzyme-linked immunoabsorbant aay(ELISA)An aay for quantifying the presence of an antigen by using an enzyme linked to an antibody to the antigen.enzymes Biological macromolecules that act as catalysts for biochemical reactions;although almost all are composed of protein, catalytically active RNA molecules have been recently discovered.enzyme-substrate complex The product of specific binding between the active site of an enzyme and the substrate.epimerases Enzymes that catalyze the interconversion of epimers of a compound.epimers Pairs of molecules, each with more than one asymmetric center, that differ in configuration at only one such center;glucose and galactose are epimers, differing only in the configuration at C-4.epinephrine(adrenaline)A catecholamine released by the adrenal medulla in response to muscle activity or its anticipation that stimulates the breakdown of muscle glycogen.epitope The specific site on an antigen that is recognized by an antibody.Also known as the antigenic determinant.equilibrium potential The equilibrium achieved when the driving force due to a concentration gradient is balanced by an electrostatic force resisting the motion of additional charges;applies to a membrane separating two different concentrations of ion with a channel connecting the two sides of the membrane.ER(endoplasmic reticulum)stre The inability of the endoplasmic reticulum of -cells of the pancreas to proce all of the proinsulin and insulin.ER stre is a precursor to pancreatic failure.erythromycin An antibiotic that binds to the 50S ribosomal subunit and inhibits peptide translocation in prokaryotes.erythropoietin(EPO)A glycoprotein hormone secreted by the kidneys that stimulates the production of red blood cells.eential amino acids Amino acids that cannot be synthesized de novo and therefore must be acquired from the diet;in adult mammals, at least nine amino acids are considered eential.eukaryote A member of the domain Eukarya.The defining characteristic of eukaryotes is the presence of a well-defined nucleus within each cell.evolutionary tree A branching diagram or ―tree‖ that shows the evolutionary relatedne of different organisms on the basis of some biological characteristic, such as the amino acid sequences of a family of proteins.exons Regions of pre-mRNA that are retained in mature mRNA.exonuclease An enzyme that digests nucleic acids from the ends of the molecule, rather than at an internal site;exonucleases can be specific for digestion from the 3' or 5' ends of the nucleic acid.expreion vector A plasmid-cloning vector that has been optimized for the expreion of large amounts of recombinant protein encoded by the vector.F

Fab fragment One of two 50-kd polypeptide chains produced when immunoglobulin G is cleaved by the protease papain;Fab fragments bind antigens but cannot cro-link them, because each fragment has only one binding site for an antigen.facilitated diffusion Transport of an ion or a molecule down a concentration gradient, where.G for the transported species is negative.Also called paive transport.FAD and FADH2(flavin adenine dinucleotide)An important electron carrier in the oxidation of fuel molecules;alternates between the oxidized FAD form and the reduced FADH2 form.It consists of a flavin moiety and an AMP unit;electrons are carried on the isoalloxazine moiety of the molecule.familial hypercholesterolemia A disease that results from the dysfunctional receptor-mediated endocytosis of cholesterol-bearing lipoprotein particles.With this disease, patients have abnormally high blood levels of cholesterol, which can lead to arterial narrowing and heart attacks at an early age.fatty acid synthase An enzyme system that catalyzes the synthesis of saturated long-chain fatty acids from acetyl CoA, malonyl CoA, and NADPH;in bacteria, the constituent enzymes of the synthase complex can be diociated when cell extracts are prepared;in mammals, all constituent enzyme activities in fatty acid synthase are part of the same polypeptide.fatty acids Carboxylic acids containing long hydrocarbon chains that are an important fuel source as well as a key component of membrane lipids.Fc fragment One of two 50-kd polypeptide chains produced when immunoglobulin G(IgG)is cleaved by the protease papain;the Fc fragment of an intact IgG molecule cannot participate in antigen binding but can mediate other important biological activities, such as complement fixation.feedback inhibition A mode of enzyme regulation in which the end product of a biosynthetic pathway inhibits the enzyme that catalyzes the first step in that pathway.feedforward stimulation The activation of an allosteric enzyme in a later stage of a pathway by the product of a reaction that takes place earlier in the reaction pathway.fermentation An ATP-generating proce in which organic compounds act as both donors and acceptors of electrons;fermentations can take place in the absence of oxygen.ferredoxin The penultimate electron acceptor in photosystem I.Reduced ferredoxin

+subsequently reduces NADP to NADPH.ferrihemoglobin Hemoglobin in which the iron component of the heme prosthetic group is in the ferric(+3)state;ferrihemoglobin cannot bind oxygen.first meengers Hormones;molecules that transduce signals from one tiue to another tiue(the target tiue)through the blood.Fischer projection A means of depicting the stereochemistry of a molecule.In a Fischer projection of a molecule, atoms joined to an asymmetric carbon atom by horizontal bonds are in front of the plane of the page, and those joined by vertical bonds are behind.flavin mononucleotide(FMN)A coenzyme for oxidation-reduction reactions derived from the vitamin riboflavin.The electron acceptor of FMN, the isoalloxazine ring, is identical with that of FAD, but FMN lacks the adenyl nucleotide component of FAD.flavins Electron carriers that use riboflavin in electron-transfer reactions;FAD, FADH2, FMN, and FMNH2 are flavins.flavoproteins Proteins tightly aociated with FAD or FMN;flavoproteins play important roles in many oxidation-reduction reactions.fluid mosaic model The description of membranes as two-dimensional solutions of oriented lipids and globular proteins.folding funnel A depiction of the thermodynamics of protein folding.The top of the funnel represents all poible denatured conformations—that is, maximal conformational entropy.Depreions on the sides of the funnel represent semistable intermediates that can facilitate or hinder the formation of the native structure, which is at the very bottom of the funnel.fractional saturation The fraction of poible binding sites of a biomolecule that are occupied.free energy A form of energy capable of doing work under conditions of constant temperature and preure.Also, a measure of the usable energy generated in a chemical reaction;denoted by the symbol G in thermodynamics.The change in free energy(.G)of a system undergoing transformation at constant preure is equal to the change in enthalpy(.H)minus the product of the absolute temperature(T)and the change in entropy(.S).furanose A five-membered heterocyclic ring formed when a monosaccharide cyclizes to form a hemiacetal or a hemiketal;the five-membered oxygen-containing ring is similar to that of furan.G

G protein A guanyl nucleotide-binding protein that is a component of intracellular signaling pathways.In the inactive state, the G protein(sometimes called a heterotrimeric G protein)is a trimeric protein consisting of αβã subunits, with the GDP bound to the α subunit.In the active state, the α protein exchanges GDP for GTP and diociates from the βã subunits.The GTP-bound α subunit propagates the signal.Signal propagation is terminated when the α subunit hydrolyzes GTP to GDP and reaociates with the βã subunits.β-galactosidase In lactose metabolism, an eential enzyme that hydrolyzes lactose into galactose and glucose.ganglioside A ceramide, common in membranes of the nervous system, in which an oligosaccharide is linked to the ceramide by a glucose residue.gap junctions Paageways between the interiors of two contiguous cells.Also known as cell-to-cell channels.GC box A component of many eukaryotic promoters, especially those from constitutively expreed genes.The consensus sequence for the GC box is 5'-GGGCGG-3'.gel electrophoresis A technique used to separate charged molecules, such as proteins and nucleic acids, which is based on the fact that such molecules will move at differing rates through a gelatinous material, such as polyacrylamide or agarose, when subjected to an electric field.Separation depends on factors such as net charge, size, and shape of the molecules.gel-filtration chromatography A separation technique based on size differences.A sample is applied to a column consisting of porous beads.Large molecules move through the column faster than small molecules because they cannot enter the beads and, thus, have a shorter path to travel.gene duplication Duplication of a gene in the proce of replication.One of the duplication products may accumulate mutations and eventually evolve into a gene with a different but related function.general acid catalysis Acid catalysis in which the source of the proton is a donor group rather than a free H+.general acid-base catalysis Catalysis in which a molecule other than water plays the role of a proton donor or acceptor.genetic code The relation between nucleic acid sequence information and protein sequence information.genomic library A collection of DNA fragments, inserted into vector molecules, that represents the entire genome of an organism.glucagon A polypeptide hormone that is secreted by the α cells of the pancreas when the bloodglucose level is low and leads to glycogen breakdown in the liver and the release of glucose to the blood.glucogenic amino acid An amino acid whose carbon skeleton, entirely or in part, can be converted into substrates for gluconeogenesis.gluconeogenesis The synthesis of glucose from noncarbohydrate precursors, including lactate, glycerol, and amino acids.glucose 6-phosphatase A membrane protein of the lumenal side of the endoplasmic reticulum that catalyzes the formation of free glucose from glucose 6-phosphate.In the liver, the enzyme plays a key role in maintaining blood-glucose levels.glucose 6-phosphate A key intermediate in metabolism that can be proceed to free glucose, stored as glycogen, oxidized to produce NADPH and ribose, or metabolized to generate cellular energy either aerobically or anaerobically.glucose 6-phosphate dehydrogenase An enzyme that initiates the oxidative phase of the pentose phosphate pathway by oxidizing glucose 6-phosphate to 6-phosphoglucono-ä-lactone to generate one molecule of NADPH.glucose homeostasis Maintenance of a constant level of glucose in the blood.glucose transporter An integral membrane protein consisting of a single polypeptide chain that has 12 transmembrane segments and facilitates the movement of glucose acro the plasma membrane into the cell.glucose-alanine cycle A cycle that allows the use of branched chain amino acids by muscle as a fuel.The nitrogen removed from the branched chain amino acids is transferred to pyruvate to form alanine, which is released into the bloodstream.In the liver, alanine is taken up and converted into pyruvate for the subsequent synthesis of glucose.glutamate dehydrogenase An enzyme that catalyzes the oxidative deamination of glutamate, yielding ammonium ion and α-ketoglutarate.glutamine phosphoribosyl amidotransferase The enzyme catalyzing the committed step in purine synthesis.The pyrophosphate of PRPP is replaced by ammonia, to produce 5-phosphoribosyl-1-amine.glutamine phosphoryl amidotransferase An enzyme that catalyzes the committed step in purine synthesis, which is the displacement of pyrophosphate in 5-phosphoribosyl-1-pyrophosphate by ammonia to yield 5-phosphoribosyl-1-amine with the amine in the β configuration.glutathione(-glutamylcysteinylglycine or GSH)A tripeptide playing a role in combating oxidative stre by maintaining the reduced state of the cell.Glutathione cycles between the reduced(GSH)and oxidized(GSSG)state.glycerol 3-phosphate shuttle A pathway that transfers electrons from cytoplasmic NADH into the mitochondria;dihydroxyacetone phosphate(DHAP)is reduced by NADH to glycerol 3-phosphate, which enters the mitochondria and is oxidized to yield FADH2 and DHAP, which leaves the mitochondria.glyceryl ether phospholipid A phospholipid that contains an ether unit rather than an acyl unit at C-1 and is synthesized starting with dihydroxyacetone phosphate rather than glycerol phosphate.glycobiology The study of the synthesis and structure of carbohydrates and how carbohydrates are attached to and recognized by other molecules such as proteins.glycoforms Forms of a specific protein that differ only in patterns of glycosylation.glycogen A readily mobilized storage form of glucose in which the glucose monomers are linked by α-1,4-glycosidic bonds and with branches(α-1,6-glycosidic bonds)at about every tenth residue.glycogen degradation The cleavage of glycogen by phosphorolysis, catalyzed by glycogen phosphorylase, to yield glucose 1-phosphate, which can be converted into glucose 6-phosphate.glycogen phosphorylase An enzyme that catalyzes the phosphorolysis of glycogen to yield glucose 1-phosphate;an allosteric enzyme whose activity is further regulated by reversible covalent modification.glycogen storage diseases Any of a number of heritable diseases characterized by an inability to store or utilize glycogen appropriately.glycogen synthase An allosteric enzyme that can be reversibly covalently regulated and is responsible for the synthesis of glycogen;it transfers glucose from UDP-glucose to the hydroxyl group at a C-4 terminus of glycogen.glycogen synthesis The synthesis of glycogen from UDP-glucose, which is catalyzed by the enzyme glycogen synthase.glycolipids Sugar-containing lipids that are derived from sphingosine;the sugar moiety is attached at the alcohol on sphingosine.glycolysis A sequence of reactions that convert glucose into pyruvate with the concomitant generation of energy.glycomics The study of the glycome, all of the carbohydrates and carbohydrate-aociated molecules that cells produce.Like the proteome, the glycome is not static and can change, depending on cellular and environmental conditions.glycoproteins Proteins that have a specific carbohydrate moiety attached.glycosaminoglycan A heteropolysaccharide made of repeating disaccharide units and containing the amino sugar glucosamine or galactosamine.glycosidase A cla of enzymes that cleave glycosidic bonds;lysozyme is a glycosidase.glycosidic bond A covalent bond between an aldehyde or ketone function of a monosaccharide and an oxygen, nitrogen, or sulfur atom of another molecule.The most common glycosidic linkages are O-links between the anomeric carbon atom of a sugar and a hydroxyl group of another saccharide.glycosyltransferase Any one of a number of specific enzymes that catalyze the formation of glycosidic bonds.glyoxylate cycle A metabolic pathway that converts two-carbon units into succinate for energy production and biosyntheses;found primarily in bacteria and plants, the cycle bypaes two decarboxylation steps in the citric acid cycle and allows the net formation of glucose and other molecules through oxaloacetate from acetate or acetyl CoA.glyoxysomes Plant organelles in which enzymes of the glyoxylate pathway are present.Golgi complex In the cytoplasm, a stack of membranous sacks that constitute the major sorting center for proteins that reside in cell membranes and the lumen of organelles.gout A disease characterized by inflammation of the joints and kidneys due to the precipitation of abnormally high levels of sodium urate, a breakdown product of purines.green fluorescent protein A protein isolated from the jelly fish Aequorea victoria that fluoresces.Because the protein can be attached to other proteins by genetic engineering techniques, it provides a means of localizing proteins in cells.group-specific reagent A chemical agent that reacts with the side chain of specific amino acid.Group-specific reagents can be used to probe protein function.group-transfer reaction A reaction in which a chemical group is transferred from one molecule to another.guanylate cyclase An enzyme that catalyzes the synthesis of cGMP, a second meenger, from GTP.H

hairpin loop A loop of nucleic acid formed by duplex formation within a single strand.Haworth projection A depiction of a cyclic carbohydrate in which the plane of each ring is perpendicular to the plane of the page and in which ring carbon atoms are not explicitly shown.HDL(high-density lipoprotein)A lipoprotein that collects cholesterol released into the blood from dying cells or from membranes undergoing turnover.heat-shock proteins A ubiquitous group of proteins that are synthesized in response to stre, such as a heat shock, and that bind unfolded polypeptides and aist in their refolding.heavy(H)chain A 50-kd polypeptide that is one of two types of paired chains found in the immunoglobulin G molecule;each heavy chain consists of a variable region and three constant regions, and each chain is linked by a disulfide bond to a light chain.heme The prosthetic group of myoglobin and hemoglobin as well as other proteins;consists of an organic constituent, protoporphyrin, and an iron atom.hemiacetal A compound formed by the reaction of an aldehyde functional group and a hydroxyl group;for example, the C-1 group of the open-chain form of glucose reacts with the C-5 hydroxyl group to form an intermolecular hemiacetal.hemiketal A compound formed by the reaction of a ketone group and a hydroxyl group;for example, the C-2 keto group of the open-chain form of fructose reacts with the C-5 hydroxyl group to form an intermolecular hemiketal.hemoglobin An allosteric protein that is the primary oxygen-carrying protein in vertebrates;it also plays a role in the transport of CO2 and H+.hemoglobin H Hemoglobin, which forms in the absence of the  chain, that consists only  chains.Hemoglobin H binds oxygen with high affinity and displays no cooperativity.hemoglobin S a mutant form of hemoglobin and the cause of sickle cell anemia that aggregates when the oxygen concentration is low, which in turn causes the red blood cells to form sickle shapes that impede blood flow in capillaries.hemophilia A general term for a number of disorders of blood clotting, in which one or another protein in the blood-clotting pathway is defective or miing.heterotropic effects The effects of nonsubstrate molecules on allosteric enzymes.hexokinase A kinase that phosphorylates six-carbon sugars, usually glucose, at the expense of ATP.hexose monophosphate pool

The mixture of fructose 6-phosphate, glucose 1-phosphate and glucose 6-phosphate present in cells.hexoses Monosaccharides that have six carbons.high-density lipoprotein(HDL)A lipoprotein that picks up cholesterol from dying cells and from membranes undergoing turnover, esterifies it, and then transfers the cholesterol esters to the liver and other steroid-synthesizing tiues.high-preure liquid chromatography A column chromatography technique in which the column materials are very finely divided and, as a consequence, poe more interaction sites and thus greater resolving power.Because the column is made of finer material, preure must be applied to the column to obtain adequate flow rates.The net result is both high resolution and rapid separation.Hill coefficient The slope of the line generated by a Hill plot.The Hill coefficient is a measure of cooperativity in ligand binding.Hill plot A plot of log(Y/1-Y)versus log(pO2), where Y is fractional saturation and pO2 is partial preure of oxygen, that can be used to determine the degree of cooperativity of oxygen binding.histone acetyltransferase(HAT)An enzyme that catalyzes the attachment of acetyl groups from acetyl CoA to specific lysine residues in the amino-terminal domains of histones.These enzymes play crucial roles in the modification of chromatin structure that enhances transcription.histone deacetylase An enzyme that contributes to transcriptional repreion by deacetylation of acetylated lysine residues in histones.histones A highly conserved group of small basic proteins found in eukaryotes in aociation with DNA to form nucleosomes.holoenzyme An enzyme that consists of the protein component forming the main body of the enzyme(the apoenzyme)and any neceary, usually small, cofactors.homotropic effects The effects of substrate molecules on allosteric enzymes.horizontal gene transfer The paing of pieces of DNA(plasmids)between species that provide a selective advantage in particular environments.human immunodeficiency virus(HIV)The cause of acquired immune deficiency syndrome(AIDS).HIV destroys helper T cells by increasing the permeability of the T cell membrane.Lo of the helper T cells severely cripples the immune system, rendering the victim susceptible to many types of infection.hydratase An enzyme that adds the elements of water to a carbon-carbon double bond.hydrogen bond A bond formed when two relatively electronegative atoms, such as oxygen or nitrogen, unequally share a hydrogen atom that is covalently bonded to one of the electronegative atoms.hydrolase A cla of enzymes that cleaves bonds by the addition of water(transfer of functional groups to water).hydrolytic reactions Reactions in which bonds are cleaved by the addition of water.hydrophobic effect The tendency of hydrophobic molecules to aociate with one another in water.The aociation is powered by the resulting increase in the entropy of water.hydrophobic interactions Refers to the tendency of nonpolar molecules in water to interact with one another;the interactions are driven by an increase in the entropy of water when the water molecules in contact with the nonpolar molecules are released into bulk water.3-hydroxy-3-methylglutaryl CoA reductase(HMG-CoA reductase)A highly regulated enzyme that catalyzes the committed step in cholesterol synthesis-the formation of mevalonate from 3-hydroxy-3-methylglutaryl CoA.hydroxyproline A derivative of proline that has a hydroxyl group in place of one of the hydrogen atoms on the pyrrolidine rings.Hydroxyproline is a key constituent of collagen.hyperammonemia A condition characterized by high levels of ammonia in the blood due to deficiencies in the urea cycle, which can result in brain damage and death.hypoxanthine A purine base that reacts with 5-phosphoribosyl-1-pyrophosphate(PRPP)to form inosinate;the reaction is part of the salvage pathway for purine nucleotides.I

IDLs(intermediate-density lipoproteins)Lipoprotein particles that remain after much of the triacylglycerides from VLDL are hydrolyzed and absorbed by other tiues;can be absorbed by the liver or converted into LDL.immunoglobulin A(IgA)The major cla of antibodies in external secretions, such as saliva, tears, bronchial mucus and intestinal mucus.immunoglobulin D(IgD)An antibody of unknown function.immunoglobulin fold A common structural motif for immunoglobulins, in which two broad sheets of antiparallel β strands enclose hydrophobic side chains, and complementarity-determining regions of variable domains pair to form an antigen-binding site.immunoglobulin G(IgG)The major antibody in serum;IgG poes two antigen-binding sites.immunoglobulin M(IgM)The first cla of antibodies to appear in the serum after exposure to an antigen;IgM poeses ten antigen-binding sites.induced fit The modification of the shape of an active site in an enzyme after the substrate is bound.induced pluripotent stem(iPS)cell Pluripotent stem cells, which have the ability to differentiate into many different cell types on appropriate treatment, generated by introducing genes encoding four transcription factors into skin cells called fibroblasts.inducer A small molecule that binds to a repreor and alters its interaction with an operator.inhibition constant A measure of the strength of binding of an inhibitor to an enzyme.Ki = [E] [I]/[EI] where [S] is the concentration of free enzyme, [I] is the concentration of free inhibitor, and [EI] is the concentration of the enzyme-inhibitor complex.inhibitor 1 A protein that, when phosphorylated, inhibits the activity of protein phosphatase 1 and thereby sustains glycogen breakdown and inhibits glycogen synthesis.initiation complex A complex of an RNA polymerase, promoter elements, and specific transcription factors that permits the initiation of RNA synthesis.initiation factor One of a set of proteins that aist in the aociation of the ribosome, mRNA, and initiator tRNA to initiate the proce of protein synthesis.initiation The first of the three stages common to all biological polymerization reactions;this stage establishes conditions for the beginning of the polymerization proce.in-line displacement A hydrolysis reaction, characteristic of restriction enzymes, in which the incoming nucleophile attacks the phosphorus atom.The transition state has a trigonal bipyramidal geometry centered at the phosphorus atom, with the incoming nucleophile at one apex of the two pyramids and the group that is displaced(the leaving group)at the other apex, in line with the incoming nucleophile.innate immune system An evolutionarily ancient defense system that responds rapidly to features present in many pathogens.The innate immune systems includes the epithelial lining that surrounds host cell, phagocytes, and a family of receptors that can recognize specific features present in most pathogens.inosinate A purine nucleotide formed by the reaction of hypoxanthine with 5-phosphoribosyl-1-pyrophosphate(PRPP);a precursor to both AMP and GMP.inositol 1,4,5-trisphosphate A second meenger of the phosphoinositide cascade that causes an increase in intracellular calcium levels.insertion A type of mutation in which one or more base pairs are erroneously inserted into DNA.insertion sequence A simple DNA transposon, composed of a kilobase sequence that specifies a transposase and is bounded on either end by inverted terminal repeats;an insertion sequence can insert itself into any site on a bacterial chromosome.insertional inactivation Gene inactivation that occurs when an unrelated DNA fragment is inserted at a restriction site;inactivation of a gene for antibiotic resistance in a plasmid can be used to detect those plasmids in which a DNA fragment has been succefully inserted.insig An integral membrane protein of the endoplasmic reticulum that binds SCAP and thereby SREBP when cholesterol levels are adequate.This binding prevents the activation of SREP and the synthesis of cholesterol.insulin A polypeptide hormone secreted by the á cells of the pancreas, that stimulates fuel storage and protein synthesis.insulin receptor A receptor tyrosine kinase that mediates the action of insulin.insulin resistance A condition marked by a normal or elevated levels of blood insulin, but cells are nonethele unresponsive to the hormone.insulin-receptor substate(IRS)Adaptor proteins that bind to phosphorylated insulin receptor and, in turn, are phosphorylated by the receptor.Other proteins bind to the phosphorylated IRS to propagate the insulin signal.integral membrane proteins Proteins found in membranes that interact extensively with the hydrocarbon chains of the membrane lipids and usually span the membrane.intercalating agents Flat, aromatic compounds that can insert between adjacent base pairs in a DNA double helix;these agents, such as ethidium bromide, can cause insertions and deletions.intermediate filaments Filaments ranging from approximately 7 to10 nm in diameter that can be components of the cell cytoskeleton in epithelial cells;keratins are intermediate filaments.intrinsic clotting pathway The-blood clotting cascade of enzyme activities that is initiated by the activation of factor XII through contact of activating proteins(kininogen and kallikrein)with abnormal cell surfaces produced by injury;at least six proteins are activated in the pathway to thrombin formation and the continuing sequence that leads to a blood clot.intrinsically unstructured protein(IUP)Proteins that, completely or in part, do not have a discrete three-dimensional structure under physiological conditions, but aume a defined structure upon interaction with other proteins.introns Regions of the primary transcript that are removed in the mature mRNA.Also called intervening sequences.inversion A nucleotide sequence whose normal order is reversed in a gene or in a chromosome.inverted terminal repeats Sequences of 20 or so base pairs at opposite ends of a bacterial insertion sequence.ion channels Paive transport systems for ions capable of very high transport rates;ion channels often display a high degree of specificity for the transported ion.ion-exchange chromatography A protein purification technique that relies on the charge of proteins.Proteins are applied to an inert matrix to which is attached a charged moiety(e.g., a carboxylate group).Proteins will bind to the matrix with an affinity proportional to their content of the counterion(i.e., positive charges in regard to the carboxylate matrix).iron-sulfur proteins Proteins that contain clusters of iron and sulfur that play a role in electron transfer reactions;iron cycles between the Fe2+ and Fe3+ state.Also called nonheme iron proteins.irreversible inhibitor An inhibitor that binds very tightly to its target enzyme, either covalently or noncovalently;such an inhibitor diociates very slowly from the enzyme.isocitrate dehydrogenase An enzyme that catalyzes the oxidative decarboxylation of isocitrate to form α-ketoglutarate;plays a role in controlling the rate of the citric acid cycle.isocitrate lyase An enzyme of the glyoxylate cycle, isocitrate lyase cleaves isocitrate into succinate and glyoxylate.isoelectric focusing A technique for separating proteins.A mixture of proteins is undergoes electrophoresis in a pH gradient;each protein will migrate in the electrical field until it reaches its isoelectric point.isoelectric point(pI)The pH of a protein at which its net charge is equal to zero.isomerase An enzyme that catalyzes the interconversion of isomeric forms of a compound.isopentenyl pyrophosphate Activated isoprene;the basic building block of cholesterol.3-isopentyl pyrophosphate A precursor to cholesterol as well as a large variety of other biomolecules such as vitamin K, coenzyme Q, and the carotenoids.Isopentyl pyrophosphate is derived from mevalonate.isopropylthiogalactoside(IPTG)An inducer of the lac operon;ITPG binds to the lac repreor and reduces the repreor's affinity for the operator DNA, which permits transcription to take place.isozymes Enzymes in an organism that catalyze the same reaction but differ in structure;these differences may range from one to several amino acid residues.Also called isoenzymes.J

joule The amount of energy needed to apply a 1-newton force over a distance of 1 meter;a kilojoule(kJ)is equal to 1000 J, or to 0.239 kcal.K

ketogenic amino acids Amino acids whose carbon skeletons, entirely or in part, are degraded into acetyl CoA or acetoacetyl CoA;only leucine and lysine are solely ketogenic.ketone body Refers to acetoacetate, β-hydroxybutyrate, and acetone, produced when acetyl CoA is diverted from the citric acid cycle to the formation of acetoacetyl CoA in the liver;subsequent reactions generate the three compounds, known as ketone bodies.ketose A monosaccharide that has a ketone group as its most oxidized carbon.α-ketoglutarate dehydrogenase A citric acid cycle enzyme that catalyzes the oxidative decarboxylation of α-ketoglutarate to yield succinyl CoA;this enzyme, which helps to regulate the rate of the citric acid cycle, is structurally and mechanistically similar to the pyruvate dehydrogenase complex.kilobase A unit of length equal to 1000 base pairs of a double-stranded nucleic acid molecule or to 1000 bases of a single-stranded molecule.kilocalorie(kcal)A unit of energy equal to 1000 calories, or 4.184 joules.kinase An enzyme that catalyzes the attachment of a phosphoryl group to a substrate by using ATP as a phosphoryl donor.Krebs cycle See citric acid cycle.L

lac operon The operon that encodes the genes required for lactose metabolism.lac repreor The regulator protein that binds to the operator site of the lac operon and thereby inhibits expreion of the structural genes of the operon;inhibition is relieved when the repreor protein binds allolactose, an inducer of the lac operon.lactic acid fermentation The anaerobic metabolism of glucose to yield lactic acid with the concomitant production of ATP.lectins Plant proteins with a high affinity for specific sugar residues;as such, they are important probes of carbohydrate-containing molecules.leptin A polypeptide hormone, secreted by the adipocytes in direct proportion to fat ma, that generates satiation signals.Lesch–Nyhan syndrome A syndrome, aociated with a lack of the purine salvage pathway enzyme hypoxanthine-guanine phosphoribosyl transferase, that is characterized by compulsive self-destructive behavior, mental deficiency, spasticity and aggreivene toward others.ligand A small molecule that binds to a protein, inducing a specific structural change.For instance, a steroid is a ligand for a steroid-hormone receptor.ligand-gated channel A transmembrane channel that is opened by the binding of a one or more molecules to a ligand-binding domain of the channel protein.light(L)chain A 25-kd polypeptide that is one of two types of chains found in immunoglobulin G.Each L chain consists of a variable region and a constant region, and each chain is linked by a disulfide bond to a heavy chain.lipid bilayer A bimolecular sheet formed by amphipathic molecules in which the hydrophobic moieties are on the inside of the sheet and the hydrophilic ones are on the aqueous outside.lipid raft Membrane structures that result when cholesterol forms specific complexes with sphingolipids, certain glycolipids, and specific GPI-anchored proteins.These complexes concentrate within small(10–200 nm)and highly dynamic regions within membranes.lipoic acid(6, 8-dithiooctanoic acid)An acyl group carrier that functions as a cofactor in dehydrogenase enzymes;linked covalently to specific lysine residues in enzyme proteins, it can exist as the reduced open-chain form or the closed-ring disulfide form, undergoing interconversion in a catalytic cycle.lipoprotein particles Particles, consisting of a core of hydrophobic lipids surrounded by a shell of polar lipids and specific proteins, that play a role in the transport of cholesterol and triacylglycerols.lovastatin A competitive inhibitor of HMG-CoA reductase, the key regulatory enzyme in cholesterol biosynthesis;used therapeutically to lower cholesterol levels.Also called mevinolin.low-density lipoprotein(LDL)The major carrier of cholesterol in the blood;consists of a core of esterified cholesterol molecules surrounded by a shell of phospholipids, unesterified cholesterol, and apoprotein B-100;primary source of cholesterol for cells other than the liver or intestine.lyase A cla of enzymes that catalyze the addition or removal of groups to form double bonds.M

major groove A 12-Å-wide, 8.5-Å-deep groove in B-DNA resulting from the fact that the glycosidic bonds of a base pair are not diametrically opposite each other.malaria A disease carried by a mosquito parasite, Plasmodium falciparum, that lives within red blood cells at one stage in its life cycle.The presence of one allele for hemoglobin S confers resistance to malaria.malate synthase An enzyme of the glyoxylate cycle that catalyzes the formation of oxaloacetate from glyoxylate and acetyl CoA.malate–aspartate shuttle A means to transport electrons from cytoplasmic NADH into the mitochondria to reform NADH.The shuttle, which is common in heart and liver, consists of two membrane carriers and four enzymes.malate-aspartate shuttle A reversible shuttle, found in the liver and heart, used to transport electrons from cytoplasmic NADH to mitochondrial NAD+.malonyl CoA The activated form of acetyl CoA required for fatty acid synthesis.Malonyl CoA also inhibits fatty acid degradation.matrix-aisted laser desorption/ionization(MALDI)A technique for determining a proteins ma.The protein is evaporated to dryne in the presence of a volatile, aromatic compound that can absorb light at specific wavelengths.A laser pulse excites and vaporizes the matrix, converting some of the protein into the gas phase.Subsequent collisions enable the intermolecular transfer of charge, ionizing the protein.The newly formed ions then enter the ma analyzer, where they are distinguished on the basis of their ma-to-charge ratios.maximal velocity The highest rate of an enzyme-catalyzed reaction, under conditions of constant enzyme concentration and saturating amounts of substrate.melting temperature The temperature at which secondary or higher structures of a biological molecule are lost;for a nucleic acid, the melting temperature is defined as the temperature at which half the helical structure is lost.membrane asymmetry Refers to the fact that the two phases of biologically important membranes differ from each other.membranes Sheetlike structures composed of lipids and proteins, usually only a few molecules thick, that form closed boundaries between different compartments;membranes separate aqueous environments

meenger RNA(mRNA)Template for protein synthesis;the base sequence of mRNA is complementary to that of a gene in DNA.metabolism A highly integrated network of chemical pathways that enables a cell to extract energy from the environment and use this energy for biosynthetic purposes.metabolite Low-molecular-weight molecules such as glucose and glycerol that are chemically transformed in biological procees.metal ion catalysis Catalysis in which a metal acts as an electrophilic catalyst by stabilizing a negative charge on a reaction intermediate, generates a nucleophile by increasing the acidity of nearby molecules, or increases the binding energy of the enzyme-substrate interaction by binding to substrates.methylases In general, an enzyme that attaches a methyl group to a molecule.Methylases modify the recognition sites for restriction enzymes in bacterial DNA in order to prevent digestion by the bacteria’s own restriction enzymes.mevalonate A precursor for the synthesis of cholesterol;its formation by HMG-CoA reductase constitutes the committed step in cholesterol biosynthesis.micelle A globular structure formed by amphipathic molecules in which the hydrophilic part is exposed to water and the hydrophobic part is sequestered inside, away from the water.Michaelis constant The concentration of substrate at which half the active sites of an enzyme are filled;a ratio of rate constants for the reaction model.E + S ES E + P, k1 k2,k-1;The constant is defined as KM = k-1+ k2/k1.Under conditions where k-1 is much greater than k2, KM is equal to the diociation constant of the enzyme-substrate complex and is a measure of the affinity of the enzyme for the substrate.Michaelis-Menten equation An equation that exprees the velocity(V)of an enzyme-catalyzed reaction in terms of maximum velocity(V/max), substrate concentration(S), and the Michaelis-Menten constant(KM).The equation accounts for the hyperbolic kinetics observed when V is plotted as a function of S;the equation is V = Vmax [S]/([S] + KM).microRNA(miRNA)RNA molecule 22-nucleotides in length that poees the regulatory activity when bound to members of a cla of proteins called the Argonaute family.microsomes Closed vesicles formed by self-annealing fragments of the endoplasmic reticulum subsequent to following cell disruption.minor groove A 6-Å-wide, 7.5-Å-deep groove in B-DNA that arises because the glycosidic bonds of a base pair are not diametrically opposite one another.mitochondrion An oval-shaped organelle, about 2 Mm in length and 0.5 Mm in diameter, that is the site of oxidative phosphorylation, the enzymes of the citric acid cycle, and the enzymes of fatty acid oxidation.monoclonal antibody An antibody derived from a clone-a large number of cells that are all descended from the same cell and have identical properties.Normally, antigens with a common specificity are heterogeneous because they are produced by a heterogeneous group of cells.Fusion of a single antigen-producing cell with an immortal myeloma cell facilitates the production of large amounts of homogeneous antibody protein, these antibodies are valuable analytical and preparative reagents.monosaccharides Single aldehydes or ketones that have two or more hydroxyl groups;the simplest carbohydrates.multienzyme complex A polypeptide chain that contains domains for two or more enzymatic activities.multifunctional enzymes Functionally related enzymes that are covalently linked in some fashion.mutarotation For carbohydrates, the interconversion of α and β anomers through the open-chain form;usually measured through changes in optical rotation.myoglobin A vertebrate oxygen-storage protein found in muscle;structurally similar to an individual hemoglobin subunit.N

N-acetylglutamate An allosteric activator of mammalian carbamoyl phosphate synthetase, which catalyses the synthesis of urea.NAD+ and NADH(nicotinamide adenine dinucleotide)An important electron carrier in the oxidation of fuel molecules;electrons are carried on the nicotinamide moiety of the coenzyme.NAD-binding domain A structural motif of NAD+-linked dehydrogenases that forms a binding site for NAD+ and consists of four helices and six parallel β strands.NADH-Q oxidoreductase A large component of the respiratory chain that transfers electrons from NADH to ubiquinone and in the proce pumps protons acro the inner mitochondrial membrane to generate the proton-motive force.Also called NADH dehydrogenase or Complex I.NADP+ and NADPH(nicotinamide adenine dinucleotide phosphate)The electron donor for reductive biosynthesis;differs from NAD+ and NADH in that a phosphate is attached to the adenine ribose at position 3.negative nitrogen balance A physiological state in which more protein is degraded than is synthesized, and so more nitrogen is excreted than is ingested.nicotinate A vitamin that is a key component of the electron-transfer coenzymes NAD+, NADH, NADP+, and NADPH.Also called niacine.nitric oxide(NO)A free-radical gas, synthesized from arginine, that is an important meenger in many vertebrate signal transduction procees.nitrogen fixation The conversion of diatomic nitrogen into ammonia;the first step in the flow of nitrogen into amino acids, nucleotides, and other nitrogen-containing compounds in organisms.noncompetitive inhibition The reduction in the rate of enzyme activity observed when an enzyme can bind its substrate and its inhibitor simultaneously.Noncompetitive inhibitors decrease the turnover number for an enzyme but do not diminish the proportion of enzyme molecules bound to the substrate;their effects are not overcome by increasing substrate concentration.noneential amino acids Amino acids that can be synthesized by an organism and are thus not a dietary requirement.nonreducing sugar A sugar that is not readily converted into a form with a free aldehyde group capable of reducing another compound.Such a conversion is prevented because the sugar forms a glycosidic bond with another compound.N-terminal rule The dependency of the half-life of a cytosolic protein on the nature of its N-terminal amino acid.nuclear magnetic resonance(NMR)spectroscopy An analytical technique that exploits intrinsically magnetic properties of certain atomic nuclei in proteins to determine the structure of a protein in solution.nucleoside A purine or pyrimidine base linked to a sugar.nucleotide A nitrogenous purine or pyrimidine base linked to a sugar, which is in turn linked to one or more phosphate groups.nucleotide kinases Enzymes that transfer the phosphoryl group of one nucleotide to another nucleotide, as in the reaction of ATP with UMP to form UDP and ADP.O

Okazaki fragments Small fragments of DNA(approximately 1000 nucleotides)that are formed on the lagging strand at the replication fork of DNA synthesis and later joined;enable 5'.3' polymerization at the nucleotide level while overall growth is in the 3'.5'direction.oligomycin An antibiotic that blocks ATP synthesis(and consequently the respiratory chain)by interfering with proton flow through the ATP synthase complex.oligosaccharides Carbohydrates composed of 2 to 12 monosaccharide units.oncogene A gene whose expreion contributes to the development of cancer.one-carbon metabolism Biochemical reactions in which tetrahydrofolate derivatives serve as donors of a variety of one-carbon units, ranging from the oxidation level of a methyl group to a formyl group;also includes reactions involving the fully oxidized carbon unit, carbon dioxide, and its carrier, biotin.operator A DNA segment that is adjacent to a group of structural genes and is the target sequence for a repreor protein;a unit of gene regulation and expreion that includes structural genes and regulatory elements recognized by one or more regulatory gene products.operon model A model of prokaryotic gene regulation that consists of an operator sequence and its aociated structural genes.β-oxidation Oxidation of the C-3 carbon atom that is β to a functional group;in the degradation of a fatty acyl CoA molecule, the sequence of oxidation, hydration, and oxidation reactions that converts a methylene group at C-3 into a β-keto group.oxidation-reduction reaction A reaction that transfers electrons.oxidative phosphorylation The proce in which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers.oxidoreductase A cla of enzymes that catalyze oxidation-reduction reaction.oxygen-binding curve A plot of the fractional saturation of oxygen binding proteins versus the concentration of oxygen.oxygen-diociation curve A plot of the oxygen-binding capacity of a protein versus the partial preure of oxygen.P

pantothenate A vitamin that is a key component of coenzyme A.partial preure The fraction of the total preure of a mixture of gases that is due to one component of the mixture.paive transport Transport of an ion or a molecule down a concentration gradient, where.G for the transported species is negative.Also called facilitated diffusion.Pasteur effect The inhibition of glycolysis by respiration, discovered by Louis Pasteur;the rate of glycolysis is lower in the presence of oxygen than under anaerobic conditions, a phenomenon largely due to the inhibition of phosphofructokinase by ATP and citrate.pentose phosphate pathway A metabolic pathway that generates NADPH and five-carbon sugars such as ribose 5-phosphate from glucose 6-phosphate;it includes oxidative reactions that produce NADPH and ribose 5-phosphates as well as nonoxidative reactions that together convert five-carbon sugar phosphates into gluconeogenic precursors of glucose 6-phosphate.Also referred to as the hexose monophosphate shunt or the phosphogluconate pathway.pentoses Monosaccharides that have five carbon atoms.peptide bond A covalent linkage formed between the α-carboxyl group of one amino acid and the α-amino group of another.Also known as an amide bond.peptide Two or more amino acids joined by peptide bonds.peptidoglycan A macromolecule that consists of linear polysaccharides cro-linked by short peptides;often found in bacterial cell walls, peptidoglycans confer mechanical support and protect bacterial cells from disruption by osmotic preure.peripheral membrane protein A protein aociated with the surface of a membrane by electrostatic and hydrogen-bond interactions.peroxidases Heme enzymes catalyzing the reduction of an alkyl peroxide to produce an alcohol and water.pH The concentration of hydrogen ions in solution.Specifically, the pH of a solution is defined +as pH =-log[H].phosphatase An enzyme that catalyzes the removal of a phosphoryl group from a substrate by hydrolysis.phosphatidate(diacylglycerol 3-phosphate)A precursor to triacylglycerols as well as many phospholipids.phosphoglyceride Phospholipids constructed on a glycerol backbone.phospholipase C The enzyme that catalyzes the cleavage of phosphatidylinositol 4,5-bisphosphate into the two second meengers, inositol 1,4,5-trisphosphate(IP3)and diacylglycerol(DAG), thereby activating the phosphoinositide cascade.phospholipases A cla of enzymes of varying specificity that catalyze the degradation of phospholipids;can function as digestive enzymes as well as components of signal-transduction pathways.phospholipids Important constituents of membranes and composed of three components: a backbone(usually glycerol or sphingosine), two fatty acid chains, and a phosphorylated alcohol.5-phosphoribosyl-1-pyrophosphate(PRPP)An activated form of ribose that accepts bases in nucleotide synthesis.phosphorolysis The cleavage of a bond by orthophosphate, as in the degradation of glycogen to glucose 1-phosphate.Ping-pong reactions See double-displacement reaction.pKa A measure of the susceptibility of a proton on an acid to removal by reaction with a base.pKa=-(log Ka), where Ka is the proton diociation constant of the acid.plasmalogens Phospholipids containing an α,β-unsaturated ether at the C-1 position of glycerol;abundant in phospholipids of the nervous system.plasmids Circular duplex DNA molecules that replicate autonomously and act as acceory chromosomes in bacteria;they carry useful genes but are disposable under certain conditions.poly(A)tail A long(as many as 250 nucleotides)polyadenylate segment added posttranscriptionally to the 3' end of most eukaryotic mRNA.polyclonal antibodies Antibodies that are the products of many different populations of antibodyproducing cells.polymerase An enzyme that catalyzes the step-by-step addition of ribo-or deoxyribonucleotide units to a polynucleotide chain.polymerase chain reaction(PCR)A method for amplifying DNA sequences by using DNA polymerase;a series of three-step cycles is employed, in which parental DNA strands are separated by heating, primers to flanking regions of the target sequence are annealed to the separated strands, and the primers are then extended by DNA synthesis.polypeptide A series of amino acids, each connected to the next in the series by a peptide bond.polysaccharides Carbohydrates composed of large numbers of linear or branched monosaccharide units;homopolysaccharides are composed of large numbers of one type of sugar, whereas heteropolysaccharides contain more than one type.pre-mRNA The unspliced, immediate product of RNA polymerase II in eukaryotes.Pribnow box A promoter component of prokaryotic genes that has the consensus sequence 5'-TATAAA-3' located 10 base pairs downstream from the transcription start site.primary active transport A proce in which the free energy of ATP hydrolysis is used to drive the movement of ions against their concentration gradients.primary meenger The information embodied in the interaction of ligand with its receptor molecule.primary structure Usually refers to the linear sequence of amino acids in a protein;more generally, the linear sequence of units that form a polymer.primase A specialized RNA polymerase that synthesizes the RNA primers for DNA synthesis.primer In the elongation of polymers, the initial segment of the polymer that is to be extended;elongation depends on the primer.primosome A complex of proteins that facilitate the unwinding of DNA and the synthesis of RNA primers, thus initiating DNA synthesis.proenzyme A zymogen, or a catalytically inactive precursor of an enzyme;a proenzyme can be converted into the active form by the hydrolysis of one or a few peptide bonds.progestagen A cla of steroid hormone, exemplified by progesterone, that prepares the uterus for implantation of the ovum;synthesized by the corpus luteum of the ovary.programmed cell death Refers to a cascade of proteolytic enzymes that result in controlled cell death in response to significant cell damage or specific development programs.Also called apoptosis.prokaryote Unicellular organisms, such as bacteria, which lack a nucleus.promoter sites A specific sequence of DNA, usually just upstream of a gene, that specifies the site and extent of transcription of the aociated gene.propeller twisting The twisting of base pairs in crystals of DNA from the coplanar conformation;enhances the stacking of bases within a strand.prostaglandins A cla of short-lived signal molecules that are 20-carbon fatty acids containing a fivemembered ring.prosthetic group A tightly bound cofactor required for a protein’s activity.protease inhibitor A drug or protein that specifically inhibits a particular proteolytic enzyme.Chemical protease inhibitors are clinically important drugs.proteases Enzymes that degrade proteins by cleaving peptide bonds.proteasomes Large protein complexes that carry out routine degradation of ubiquitinated cellular proteins as well as of those from pathogens.protein A biological macromolecule composed of a linear array of amino acids joined by peptide bonds;roles of proteins in biological procees include catalysis, transport and storage, motion, mechanical support, immune protection, the generation and transmiion of nerve impulses, and the control of growth and differentiation.Protein Data Bank(PDB)A Web storage site for the coordinates of protein structures that have been solved by x-ray crystallography and NMR analysis.With the use of the coordinates, the structures can be acceed for visualization and analysis.protein disulfide isomerase An enzyme that catalyzes the formation of correct disulfide pairings in nascent proteins;preferentially reacting with peptides that contain cysteine residues but otherwise undiscriminating, the enzyme speeds up the disulfide shuffling required for a protein to find the most thermodynamically stable disulfide pairings among those that can be formed.protein kinase A(PKA)A protein kinase that consists of two catalytic subunits and two regulatory subunits that inhibit the catalytic subunits;on binding of cAMP, the regulatory subunits diociate from the catalytic subunits, which then become active.protein kinase C(PKC)A protein kinase that is activated by the binding of diacylglycerol.protein kinases A cla of enzymes that transfer a phosphoryl group from ATP to proteins;protein kinases are frequently found in regulatory pathways.protein phosphatases Enzymes that hydrolyze phosphorylated serine and threonine residues in other proteins;protein phosphatase 1 reverses the regulatory effects of kinases on glycogen metabolism.proteoglycans Proteins containing one or more covalently linked glycosaminoglycan chains;cartilage proteoglycan contains keratan sulfate and chondroitin chains linked to a polypeptide backbone.proteome The functional representation of the genome that includes the types, functions, and interactions of proteins that are present in a cell;the proteome is not a fixed characteristic of a cell but will vary, depending on such factors as developmental stage or hormonal status.proton gradient The unequal distribution of protons acro a proton-impermeable membrane;such gradients can be used to power various biochemical procees, such as the synthesis of ATP.proton-motive force The energy inherent in the proton gradient established during the functioning of the respiratory chain;consists of a membrane potential as well as a chemical gradient.proto-oncogene A signal transduction protein that usually regulates cell growth in some fashion;when proto-oncogenes mutated, they become oncogenes and contribute to the development of cancer.protoporphyrin An organic constituent of the heme prosthetic group;consists of four pyrrole rings joined by methylene bridges and contains various side chains.proximal histidine The histidine that binds the fifth coordination site of the heme in myoglobin and hemoglobin.pseudogenes Sequences of DNA that resemble actual genes but do not encode functional products.pseudosubstrate An amino acid sequence that resembles the actual substrate for an enzyme except that a crucial amino acid has been changed, converting the sequence into an inhibitor;the regulated binding of pseudosubstrates is sometimes used to control enzyme activity.pump A protein paage in a membrane that can transport a molecule from one compartment to another against a concentration gradient;pumps undergo a cycle of conformational changes that alter the affinity of the binding site for the transported molecule, and the eversion of the molecule during the cycle is driven by expenditure of free energy.Also called active transporters.purine A nitrogenous base that includes a pyrimidine ring fused with a five-membered imidazole ring;the purine derivatives adenine and guanine are found in nucleotides and nucleic acids.pyranose A six-membered heterocyclic ring formed when a monosaccharide cyclizes to form a hemiacetal or a hemiketal;the six-membered, oxygen-containing ring is similar to that of pyran.pyridine nucleotides Nucleotides, such as NAD+, NADH, NADP+, and NADPH, that are employed in redox reactions;the functional group is nicotinamide, a derivative of pyridine.pyridoxal phosphate(PLP)A prosthetic group derived from vitamin B6(pyridoxine)that plays a key role in transamination reactions.pyridoxamine phosphate(PMP)An aminated form of pyridoxal phosphate that is an intermediate in transamination reactions.pyrimidine A nitrogenous base that is a six-membered heterocyclic ring containing two nitrogen atoms and four carbon atoms;the pyrimidine derivatives cytosine, uracil, and thymine are found in nucleotides and nucleic acids.pyruvate A prominent intermediate in metabolism;a precursor for alanine and glucose and can be converted into lactate in anaerobic glycolysis;can also be oxidized to acetyl CoA, which can be further oxidized to yield energy aerobically, converted into fats, or used to synthesize cholesterol and other steroids.pyruvate carboxylase A biotin-dependent enzyme that catalyzes the formation of oxaloacetate from pyruvate and CO2 at the expense of ATP;important in gluconeogenesis as well as in the replenishment of the citric acid cycle.pyruvate dehydrogenase complex A large, complex mitochondrial enzyme that catalyzes the oxidative decarboxylation of pyruvate to form acetyl CoA;this irreversible reaction is the link between glycolysis and the citric acid cycle.pyruvate dehydrogenase kinase(PDK)A component of the pyruvate dehydrogenase complex in eukaryotes that phosphorylates and inhibits the pyruvate dehydrogenase component of the complex.pyruvate dehydrogenase phosphatase(PDP)A component of the pyruvate dehydrogenase complex in eukaryotes that dephosphorylates and activates the pyruvate dehydrogenase component of the complex.pyruvate kinase A key regulatory enzyme in glycolysis that catalyzes the formation of ATP and pyruvate from phosphoenolpyruvate and ADP.Q

Q cycle A set of reactions in which coenzyme Q cycles between the fully reduced state and the fully oxidized state through one-electron transfer reactions in which one of the electrons is temporarily stored in cytochrome b;provides a means of paing the two electrons of coenzyme Q to the single-electron carrier cytochrome c, one electron at a time.Q-cytochrome c oxidoreductase A component of the respiratory chain, this oxidoreductase carries electrons from coenzyme Q to cytochrome c and, in the proce, pumps protons out of the mitochondrial matrix to generate the proton-motive force.Also called cytochrome reductase or Complex III.quantitative PCR(qPCR)A polymerase chain reaction-based technique for determining the amount of individual mRNA molecules present in a population of RNA molecules.quaternary structure In proteins containing more than one polypeptide chain, the spatial arrangements of those chains(subunits)and the nature of contacts among them.R

R state The more active state of allosteric proteins, which is in equilibrium with the le active T-state.random-coil conformation The disordered, unfolded structure of a denatured macromolecule;many proteins that are not cro-linked lose their native three-dimensional structure as well as their biological function in the presence of unfolding agents such as urea.Ras A member of a cla of signal transduction proteins called small G proteins.These proteins bind GDP in their inactive forms and GTP in their active forms.recombinant DNA technology An array of techniques used to analyze and manipulate DNA;these methods include the specific modification of genes as well as the construction of new ones, gene cloning and amplification, and the expreion of new and modified genes to yield protein products.recombination The formation of new arrangements of genes or gene sequences by movement of DNA.reducing sugars Sugars that convert into a form with a free aldehyde group that is readily oxidized and can thus reduce another compound.reductase An enzyme that catalyzes the reduction of a functional group, often using NADPH as an electron donor;a type of oxidoreductase.regulatory proteins Proteins that bind to enzymes and regulate their catalytic activity.relaxed DNA A circular DNA molecule that has no superhelical turns.respiration An ATP-generating proce in which an inorganic compound, such as O2, serves as the ultimate electron acceptor;the electron donor can be either an organic compound or an inorganic one.respiratory chain The path that electrons travel in going from NADH or FADH2 to O2;consists of three complexes that pump protons as a result of the electron transport and two mobile electron carriers.Also called the electron transport chain.respiratory control Tight coupling or coordination of the oxidation of reduced cofactors(NADH and FADH2)in the electron-transport chain and the phosphorylation of ADP to yield ATP in the mitochondrion;such control ensures that the rate of the citric acid cycle, where reduced cofactors are generated, corresponds to the demand for ATP.restriction enzymes Endonuclease enzymes that recognize specific base sequences in double-stranded DNA and cleave both strands of the duplex at specific places.restriction-fragment-length polymorphism(RFLP)The genetic diversity within a population indicated by mutations within specific sites in DNA;such mutations alter the position of restriction fragments in electrophoretic gel analysis.retinal The prosthetic group of rhodopsin that, upon absorbing light, undergoes an isomerization from 11-cis-retinal to all-trans-retinal, initiating the visual signal transduction pathway.retrovirus A virus that contains an RNA genome but that replicates through the intermediacy of double-stranded DNA that is integrated into the host-cell genome.reverse cholesterol transport The retrieval of cholesterol from peripheral tiues by HDL for return to the liver for excretion as bile or in the feces.reverse transcriptase An enzyme that synthesizes DNA by using an RNA template.riboflavin A vitamin component of the electron-transfer coenzymes FAD, FADH2, FMN, and FMNH2.Also called vitamin B2.ribonucleotide A nucleotide that contains a purine or pyrimidine base covalently linked to a ribose, which is in turn linked to one or more phosphate groups.ribonucleotide reductase An enzyme that catalyzes the reduction of all four ribonucleotides to deoxyribonucleotides.ribose A five-carbon monosaccharide(C5H10O5)that constitutes the carbohydrate moiety of ATP, other ribonucleosides and ribonucleotides, and cofactors such as NAD and coenzyme A.ribosomal RNA The RNA component of a ribosome, the site of protein synthesis.ribosome A large ribonucleoprotein aembly that catalyzes the formation of peptide bonds;a molecular machine that coordinates protein synthesis.ribozymes RNA molecules that display enzymatic activity.rickets A disease caused by the insufficient formation of vitamin D, resulting in the inadequate calcification of cartilage and bone.rifamycin An antibiotic isolated from Streptomyces that inhibits the initiation of RNA synthesis by blocking the formation of the first phosphodiester bond.RNA enzymes RNA molecules that act as enzymes.Also called ribozymes.RNA interference The suppreion of the transcription of a gene following the introduction into the cell of double stranded RNA molecule that contained sequences present in the suppreed gene.RNA polymerases A cla of enzymes that synthesize RNA molecules complementary to a DNA template.RNA primers Small pieces of RNA that base-pair with the template strand of DNA and serve as primers for primer-dependent DNA synthesis;the RNA is later removed and replaced by DNA.RNA proceing Any alteration of a precursor RNA molecule, such as splicing or polyadenylation, that yields a mature RNA molecule.31 RNA splicing The removal of introns and the ligation of exons from precursors of RNA to form mature RNA.RNA world A theoretical time early in evolution in which RNA molecules served both as the genetic material and as catalysts for biochemical reactions.RNA-induced silencing complex(RISC)An aembly of specific proteins that facilitate the proce of RNA interference.Romann fold A common nucleotide-binding domain in proteins that is made up of four  helices and a sheet of six parallel  strands.rotenone A plant toxin that inhibits electron transfer in the NADH-Q reductase complex;used as a fish and insect poison.S

S-adenosylmethionine(SAM)An activated methyl donor that consists of an adenosyl group linked to the sulfur atom of methionine.salting out A protein purification technique based on the fact that the solubility of most proteins is lowered at higher salt concentrations;consequently, different proteins will precipitate at varying salt concentrations.salvage pathway In general, a pathway that synthesizes the final product from preformed components;nucleotides can be synthesized in a salvage pathway by attaching purine bases to PRPP.Schiff base An intermediate formed when an amine reacts with an aldehyde or a ketone from a nitrogen compound analogous to a carbonyl compound;Schiff bases are intermediates in a number of enzymecatalyzed reactions.scurvy A disease caused by a deficiency of ascorbate(vitamin C), which results in the formation of unstable collagen.SDS-polyacrylamide gel electrophoresis The electrophoresis of proteins in a polyacrylamide medium;the detergent SDS renders the movement of the proteins inversely proportional to molecular weight(see also electrophoresis).second meenger A small signal molecule whose concentration changes in response to a primary meenger.secondary structure In a protein, the spatial arrangement of amino acid residues that are relatively close to one another in the linear sequence;the α helix and the β strand are both elements of primary structure.secondary transporter A transporter that uses the energy of the downhill(exergonic)flow of one ion or molecule to power the uphill(endergonic)flow of another.Also called cotransporter.semiconservative replication In the duplication of DNA, one of the strands of each daughter molecule is newly synthesized, whereas the other is unchanged from the parental DNA double helix.sequence alignment A means of determining the evolutionary relatedne of two proteins in which the two amino acid sequences are systematically aligned with respect to each other to identify regions of significant overlap.sequential model A model for explaining allosteric enzymes in which the binding of one substrate influences the substrate affinity of neighboring active sites without necearily inducing a transition encompaing the entire enzyme.32 sequential reactions A bisubstrate reaction in which both substrates must bind to the enzyme before any product is released.Consequently, a ternary complex of the enzyme and both substrates is a reaction intermediate.SH2 domain(Src homology domain)A domain of approximately 100 amino acids that binds to phosphotyrosine residues.SH3 domain(Src homology domain)A domain that binds proline-rich stretches of polypeptide.sheet, β A common structural motif in proteins, in which two or more β strands are aociated as stacks of chains, stabilized by interchain hydrogen bonds;several β strands running in the same direction form a β pleated sheet, whereas such strands running in opposite directions form an antiparallel pleated sheet.Shine-Dalgarno sequence In meenger RNA, a purine-rich region about 10 nucleotides on the 5' side of an initiator codon that pairs with the 3' end of 16S RNA in the 30S ribosomal subunit;helps to determine where translation is initiated on an mRNA molecule.sickle-cell anemia Anemia caused by a mutation in hemoglobin that promotes aggregation of the hemoglobin when oxygen concentration is low, which in turn causes the red blood cells to form sickle shapes.Such deformed cells to not remain in circulation, thus accounting for the anemia.side chain The distinctive R group bonded to the á-carbon atom of an amino acid.sigmoid Activity curves, such as for oxygen binding or enzyme activity, that show low activity with respect to the x-axis initially and then increase rapidly, thereby generating an ―S‖ shaped curve.signal peptidase A peptidase that resides in the lumen of the endoplasmic reticulum that cleaves signal sequences from nascent polypeptide chains synthesized by endoplasmic reticulum bound ribosomes.signal sequences A sequence of amino acid residues ranging in size from 13 to 36 residues, usually at the amino terminus of the nascent polypeptide chain, that marks the protein for translocation acro the rough endoplasmic reticulum.simple diffusion The movement of lipophilic molecules through a membrane down their concentration gradient.small interfering RNA(siRNA)A cla of small RNA molecules that bind to mRNA and facilitate its degradation.small nuclear RNAs(snRNAs)A cla of small RNAs confined to the nucleus;some play a role in splicing.++++sodium-potaium pump(Na–K pump)(Na–KATPase)An enzyme that uses the energy of ATP hydrolysis to pump sodium out of the cell and potaium into the cell.Also called sodium-potaium ATPase.solid-phase method A means of synthesizing discrete peptides in which amino acids are added step-bystep to a growing peptide chain that is anchored to an insoluble matrix.Southern blotting A technique used to locate and identify a DNA fragment containing a specific sequence;a mixture of fragments is separated by electrophoresis, transferred to a nitrocellulose sheet, hybridized to a radioactively labeled DNA probe complementary to the desired sequence, and visualized by autoradiography.specific activity A measure of the activity of a protein sample relative to the amount of protein present in the sample, usually presented as activity units per milligram of protein;aeed at each step of a protein purification procedure as a measure of the effectivene of the purification.33 sphingolipid A phospholipid whose backbone is sphingosine rather than glycerol.Spingolipids are present in all eukaryotic cells, although their concentration is highest in cells of the central nervous system.They are also prominent components of lipid rafts.sphingomyelin Common in brain tiue, a sphingolipid in which the terminal hydroxyl group of ceramide has a phosphorylcholine substituent.sphingosine An amino alcohol containing a long, unsaturated hydrocarbon chain that is a component of the phospholipid sphingomyelin as well as glycolipids;serves a role analogous to that of glycerol in phosphoglycerides.standard free-energy change The free-energy change of a reaction, when it takes place under standard conditions, in which each of the reactants is present at a concentration of 1.0 M.starch A homopolysaccharide that is a storage form of glucose in plant chloroplasts;amylopectin, the branched form of starch, has approximately one α-1,6 linkage per thirty α-1,4 linkages, whereas amylose is unbranched, composed of glucose residues in α-1,4 linkage.start codon The first codon to be translated, usually AUG.statins Inhibitors of HMG-CoA reductase that are used to lower the plasma cholesterol level of people with atherosclerosis.steroid hormones Hormones, such as androgen and estrogen, derived from cholesterol.sticky ends Complementary single-stranded ends, also called cohesive ends, produced by restriction enzymes that cleave their palindromic target sequences in a staggered fashion.stop codons A set of codons that are recognized by release factors and mark the end of translation.strand, β An extended polypeptide chain, with an axial distance of 3.5 Å between adjacent amino acids, often found in a β pleated sheet.streptomycin A highly basic trisaccharide antibiotic that causes both the inhibition of translational initiation and the misreading of mRNA in prokaryotes.stringent response In bacteria, a decrease in the rate of ribosomal and transfer RNA synthesis in response to a scarcity of amino acids.substrate A reactant in a chemical reaction.An enzyme catalyzes a single chemical reaction or set of closely related reactions, and the components of those reactions are called substrates.substrate cycle A pair of thermodynamically irreversible biochemical reactions that simultaneously produce and consume a pair of metabolic intermediates;these paired pathways may amplify metabolic signals and in some cases can also generate heat for the maintenance of temperature in tiues.Also called futile cycle.substrate-level phosphorylation The formation of ATP from ADP in which the phosphate donor is a substrate with high phosphoryl transfer potential.subunit Any of the polypeptide chains in a protein that contains more than one of such chains.subunit, 30S The small subunit of the bacterial 70S ribosome;composed of 21 different proteins and a 16S RNA molecule.subunit, 50S The large subunit of the bacterial 70S ribosome;the site of peptide-bond synthesis, it contains 34 different proteins, a 5S RNA species, and a 23S RNA species.succinate-Q reductase An integral membrane protein complex of the inner mitochondrial membrane that transfers electrons from FADH2 formed in the citric acid cycle to coenzyme Q.Also called Complex II.succinyl CoA synthetase(succinate thiokinase)A citric acid cycle enzyme that catalyzes the cleavage of the thioester bond of succinyl CoA, which is coupled to the phosphorylation of a purine nucleoside diphosphate, usually ADP.34 sucrose A disaccharide of glucose and fructose(commonly known as table sugar)that is readily transportable and stored in many plant cells.-superoxide anion(O 2˙)A reactive oxygen species that can damage many biological materials.symporter A transport system in which a molecule is carried acro a membrane in the same direction as an ion, which in turn is pumped back acro the membrane through active transport linked to ATP consumption.synthase An enzyme catalyzing a synthetic reaction in which two units are joined without the direct participation of a nucleotide triphosphate.synthetase An enzyme catalyzing a synthetic reaction in which two units are joined with the direct participation of ATP or another nucleoside triphosphate.T

T state The le active state of allosteric proteins, which is in equilibrium with the more active R-state.tandem ma spectrometry The utilization of two ma analyzers to determine protein sequence.Ions of proteins that have been analyzed by a ma spectrometer are broken into smaller peptide chains by bombardment with atoms of an inert gas such as helium or argon.These new fragments can be paed through a second ma analyzer for further ma characterization.Tangier disease A disease characterized by HDL deficiency, accumulation of cholesterol in macrophages, and premature atherosclerosis.Tangier disease is due to inefficient reverse cholesterol transport, resulting from a lack of a cholesterol transport protein.TATA box Found in nearly all eukaryotic genes, a promoter element giving rise to mRNA.The TATA box is centered between 30 and 90 residues downstream of the transcription start site and has the consensus sequence 5'-TATAAAA-3'.Tay-Sachs disease A disease, caused by a failure to degrade gangliosides, in which the affected infant displays weakne and retarded psychomotor skills before 1 year of age.The child is demented and blind by age 2 and usually dies before age 3.Tay-Sachs disease A heritable disorder caused by the accumulation of gangliosides due to the lack of an enzyme(α-N-acetylhexosaminidase)responsible for their degradation;clinical characteristics include weakne, mental retardation, dementia, blindne, and death by age 3.telomerase A reverse transcriptase that contains its own template;a highly proceive enzyme that elongates the 3'-ending strand of a telomere.telomeres Ends of chromosomes;the DNA at the telomere consists of hundreds of repeats of a hexanucleotide sequence characteristic of the organism.template strand The strand of DNA that is complementary to the RNA transcript.tertiary structure In proteins, the spatial arrangement of amino acid residues that are far from each other in the linear sequence, as well as the pattern of disulfide bonds.tetracycline An antibiotic that binds to the prokaryotic 30S ribosomal subunit and inhibits the binding of aminoacyl-tRNA molecules to the ribosomal complex.tetrahydrofolate(tetrahydropteroylglutamate)A highly versatile carrier of activated one-carbon units.tetrodotoxin A highly potent poison from the fugu(puffer)fish that blocks the conduction of nerve impulses along axons and excitable membranes in nerve fibers, leading to respiratory paralysis.tetroses Monosaccharides that have four carbon atoms.35 thalaemias Genetic disorders characterized by the defective synthesis of one or more hemoglobin chains.thermogenin A mitochondrial membrane protein(an uncoupling protein)that plays a role in thermogenesis by forming a pathway for the flow of protons into the mitochondria, thereby generating heat without synthesizing ATP.thiamine pyrophosphate The coenzyme form of thiamine(vitamin B1), composed of a modified thiazole ring linked by a methylene bridge to a substituted pyrimidine;a cofactor in enzymatic reactions in which bonds to carbonyl carbon atoms are cleaved or synthesized.thiamine The vitamin component of the coenzyme thiamine pyrophosphate.Also called vitamin B1.thioredoxin A protein with exposed cysteines that can be reversibly oxidized and reduced;an important electron carrier in the reduction of ribonucleotides and in photosynthesis.thymidylate synthase An enzyme that catalyzes the methylation of deoxyuridylate(dUMP)to form thymidylate(TMP).Toll-like receptor(TLR)A family of receptors that recognize specific features present in most pathogens and yet not respond to materials normally present in the host.transaldolase An enzyme that transfers a three-carbon dihydroxyacetone unit from a ketose to an aldose acceptor;one of the enzymes in the nonoxidative part of the pentose phosphate pathway.transamination The transfer of an α-amino group from an amino acid to an α-ketoacid.transcription DNA-directed synthesis of RNA catalyzed by RNA polymerase.transcription factor A protein that aists RNA polymerase in the initiation of RNA synthesis;binds to a specific promoter element.transfer RNA(tRNA)The adaptor molecule in protein synthesis;contains an amino acid recognition site as well as a template-recognition site, or anticodon.transferase An enzyme that catalyzes group transfer, often employing a cofactor.transferrin A transport protein that carries iron in the blood serum.transferrin receptor A membrane protein that binds iron-loaded transferrin and initiates its entry into cells.transgenic mouse A mouse that harbors a foreign gene.Transgenic mice are a powerful means of exploring the role of a specific gene in the development, growth, and behavior of an entire organism.transition A mutation that results from the substitution of one pyrimidine for another or one purine for another.transition state A chemical species that has the highest free energy and the lowest concentration of those on the pathway from a substrate to a product.transition-state analog A compound resembling the transition state of a catalyzed reaction;such compounds are often potent inhibitors of enzyme-catalyzed reactions.transketolase An enzyme that transfers an activated aldehyde unit from a ketose to an aldose acceptor;one of the enzymes in the nonoxidative part of the pentose phosphate pathway.translation Cellular protein synthesis, so named because the four-letter alphabet of nucleic acids is translated into the different amino acids that make up proteins.transposons Mobile bacterial genetic elements that enable genes to be transferred among nonhomologous sequences.transversion A mutation in which a purine is replaced by a pyrimidine or vice versa.36 triacylglycerols(neutral fats, triacylglycerides)Glycerols that have fatty acyl chains esterified to each of their hydroxyl groups;storage form of fats.Also known as neutral fats or triglycerides.trioses Monosaccharides that have three carbon atoms.tumor-suppreor gene Genes for DNA-repair proteins that suppre tumor development when at least one copy of the gene is free of a deleterious mutation.turn, β In proteins, a structural element composed of four amino acids, in which the CO and NH groups of residue 1 are hydrogen bonded to the NH and CO groups of residue 4, respectively;such a structure forms a hairpin turn, allowing polypeptide chains to reverse their direction.turnover number The number of substrate molecules converted into product by an enzyme molecule in a unit time when the enzyme is fully saturated with substrate;equal to the kinetic constant k2(see Michaelis constant).two-dimensional electrophoresis A protein separation technique that separates proteins by isoelectric focusing in one direction followed by SDS-polyacrylamide gel electrophoresis at 90O to the direction of first separation.two-dimensional gel electrophoresis A means of analyzing a protein sample in which the sample is initially fractionated in one dimension by isoelectric focusing and is subsequently fractionated in a second dimension, perpendicular to the first, by SDS-polyacrylamide gel electrophoresis.type 1 diabetes Diabetes that results from the autoimmune destruction of the insulin-secreting  cells in the pancreas and usually begins before age 20.Type 1 diabetes is also referred to as insulin-dependent diabetes, meaning that the affected person requires the administration of insulin to live.type 2 diabetes The most common metabolic disease in the world, which is characterized by insulin resistance.Type 2 diabetes typically arises later in life than type 1 diabetes and its appearance is correlated with obesity.tyrosine kinase A kinase that catalyzes the transfer of a phosphoryl group from ATP to the hydroxyl group of tyrosine.U

ubiquitin Present in all eukaryotes, a small, highly conserved protein that, when attached to another protein, targets it for proteolytic destruction.ultracentrifugation High-speed centrifugation used to separate biomolecules and determine their maes.uncoupling protein A mitochondrial membrane protein that plays a role in thermogenesis by forming a pathway for the flow of protons into the mitochondria, thereby generating heat without synthesizing ATP.Also called thermogenin.unfolded protein response A signal pathway triggered by ER stre that consists of several steps.First, general protein synthesis is inhibited so as to prevent more proteins from entering the ER.Second, chaperone synthesis is stimulated.Third, misfolded proteins are removed from the ER and are subsequently delivered to the proteasome for destruction.Finally, if the described response fails to alleviate the ER stre, apoptosis is triggered, which ultimately leads to cell.uniporter A cla of carriers able to transport a specific species in either direction governed only by concentrations of that species on either side of the membrane.urea cycle A cyclic pathway that converts exce ammonia into urea for secretion;the first metabolic pathway to be discovered.37 ureotelic Refers to organisms in which exce ammonia is converted into urea and then excreted;most terrestrial vertebrates are ureotelic.uricotelic Refers to organisms in which exce ammonia is converted into the purine uric acid for secretion;birds and terrestrial reptiles are uricotelic.uridine diphosphate glucose(UDP-glucose)The activated form of glucose used in the synthesis of glycogen;formed from glucose 1-phosphate and UTP.V

van der Waals interaction The attraction between two molecules based on transient electron asymmetry around an atom that induces a complementary asymmetry in a nearby molecule.vector A DNA molecule that can replicate autonomously in an appropriate host organism.Vectors are designed to enable the rapid, covalent insertion of DNA fragments of interest.virus A complex of protein and nucleic acid that can penetrate a cell and replicate itself by co-opting the host's metabolism and employing its own as well as the host's gene products;the smallest organism known.vitamin A A fat-soluble vitamin that is the precursor of the light-sensitive pigment retinal and the signal molecule retinoic acid, an activator of certain transcription factors.Also called retinol.vitamin B12(cobalamin)A prosthetic group, consisting of a cobalt atom, a corrin ring, and deoxyadenosine, that plays a role in intramolecular rearrangements, methylations, and reductions of ribonucleotides to deoxyribonucleotides.Also called cobalamin.vitamin D A fat-soluble vitamin that plays a role in the regulation of calcium and phosphorus metabolism;deficiencies in vitamin D lead to the impairment of bone formation.vitamin E Protects unsaturated membrane lipids from oxidation.Also called α-tocopherol.vitamin K A fat-soluble vitamin required for blood coagulation.vitamins Organic substances required in trace amounts for a number of eential biochemical reactions.VLDLs(very low density lipoproteins)Lipoprotein particles, stabilized by apolipoproteins B-100 and E, that transport exce endogenous triacylglycerides and cholesterol from the liver to other tiues.voltage-gated channel A transmembrane channel that is opened by membrane depolarization;the sodium and potaium channels of axon membranes are good examples.W

Watson-Crick helix See B-DNA helix.western blotting An immunoaay technique used to detect a specific protein in a cell or in body fluid.A sample undergoes electrophoresis in an SDS-polyacrylamide gel, the resolved proteins are transferred to a polymer sheet, and then an antibody specific for the protein of interest is incubated with the blotted sample;other antibodies or radioactive markers may then be used to help visualize the desired antigen-antibody complex.X

x-ray crystallography A technique for determining the three-dimensional structure of protein crystals at atomic resolution by examining the diffraction pattern of x-rays striking the crystal.Y

yeast artificial chromosome(YAC)A DNA molecule that can be used to clone DNA inserts ranging from 100 to 1000 kb in length;contains a centromere, an autonomously replicating sequence, a pair of telomeres, selectable marker genes, and an insertion site for the sequence to be cloned.Z

Z-DNA A left-handed double helix in which the backbone phosphates zigzag;can be formed by oligonucleotides with alternating sequences of purines and pyrimidines.zwitterion A dipolar ion(from the German zwitter, “between”);at neutral pH, amino acids have a protonated amino group and a diociated carboxyl group and are therefore zwitterions.zymogen A catalytically inactive precursor of an enzyme.39