10 Генетическая инженерия (1160079), страница 12
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It does not affect the equilibriumof the catalyzed reaction; it enhances therate of a reaction by providing a reactionpath with a lower activation energy.epimerases: Enzymes that catalyze thereversible interconversion of two epimers.epimers: Two stereoisomers differing inconfiguration at one asymmetric center, ina compound having two or more asymmetric centers.epithelial cell: Any cell that forms partof the outer covering of an organism ororgan.epitope: An antigenic determinant; theparticular chemical group or groupswithin a macromolecule (antigen) to whicha given antibody binds.equilibrium: The state of a system inG-5which no further net change is occurring;the free energy is at a minimum.equilibrium constant (ifeq): A constant,characteristic for each chemical reaction;relates the specific concentrations of allreactants and products at equilibrium at agiven temperature and pressure.erythrocyte: A cell containing largeamounts of hemoglobin and specialized foroxygen transport; a red blood cell.Escherichia coli: See E.
coli.essential amino acids: Amino acids thatcannot be synthesized by humans (andother vertebrates) and must be obtainedfrom the diet.essential fatty acids: The group of polyunsaturated fatty acids produced byplants, but not by humans; required inthe human diet.ethanol fermentation: See alcohol fermentation.eukaryote: A unicellular or multicellularorganism with cells having a membranebounded nucleus, multiple chromosomes,and internal organelles.excited state: An energy-rich state of anatom or molecule; produced by the absorption of light energy.exergonic reaction: A chemical reactionthat proceeds with the release of free energy (that is, for which AG is negative).exocytosis: The fusion of an intracellularvesicle with the plasma membrane, releasing the vesicle contents to the extracellular space.exon: The segment of a eukaryotic genethat encodes a portion of the final productof the gene; a portion that remains afterposttranscriptional processing and is transcribed into a protein or incorporated intothe structure of an RNA.
See intron.exonuclease: An enzyme that hydrolyzesonly those phosphodiester bonds that arein the terminal positions of a nucleic acid.exothermic reaction: A chemical reaction that releases heat (that is, for whichAH is negative).expression vector: See vector.facilitated diffusion: Diffusion of a polarsubstance across a biological membranethrough a protein transporter; also calledpassive diffusion or passive transport.facultative cells: Cells that can live inthe presence or absence of oxygen.G-6GlossaryFAD (flavin adenine dinucleotide):The coenzyme of some oxidation—reduction enzymes; it contains riboflavin.fatty acid: A long-chain aliphatic carboxylic acid found in natural fats and oils;also a component of membrane phospholipids and glycolipids.feedback inhibition: Inhibition of an allosteric enzyme at the beginning of a metabolic sequence by the end product of thesequence; also known as end-product inhibition.fermentation: Energy-yielding anaerobicbreakdown of a nutrient molecule, such asglucose, without net oxidation; yields lactate, ethanol, or some other simple product.fibroblast: A cell of the connective tissuethat secretes connective tissue proteinssuch as collagen.fibrous proteins: Insoluble proteins thatserve in a protective or structural role;contain polypeptide chains that generallyshare a common secondary structure.fingerprinting: See peptide mapping.first law of thermodynamics: The lawstating that in all processes, the total energy of the universe remains constant.Fischer projection formulas: See projection formulas.5' end: The end of a nucleic acid thatlacks a nucleotide bound at the 5' positionof the terminal residue.flagellum: A cell appendage used in propulsion.
Bacterial flagella have a muchsimpler structure than eukaryotic flagella,which are similar to cilia.flavin-linked dehydrogenases: Dehydrogenases requiring one of the riboflavincoenzymes, FMN or FAD.flavin nucleotides: Nucleotide coenzymes (FMN and FAD) containing riboflavin.flavoprotein: An enzyme containing aflavin nucleotide as a tightly bound prosthetic group.fluid mosaic model: A model describingbiological membranes as a fluid lipid bilayer with embedded proteins; the bilayerexhibits both structural and functionalasymmetry.fluorescence: Emission of light by excited molecules as they revert to theground state.FMN (flavin mononucleotide): Riboflavin phosphate, a coenzyme of certain oxidation-reduction enzymes.footprinting: A technique for identifyingthe nucleic acid sequence bound by aDNA- or RNA-binding protein.frame shift: A mutation caused by insertion or deletion of one or more paired nucleotides, changing the reading frame ofcodons during protein synthesis; the polypeptide product has a garbled amino acidsequence beginning at the mutated codon.free energy (G): The component of thetotal energy of a system that can do workat constant temperature and pressure.free energy of activation (AG*): Seeactivation energy.free-energy change (AG): The amountof free energy released (negative AG) orabsorbed (positive AG) in a reaction atconstant temperature and pressure.free radical: See radical.functional group: The specific atom orgroup of atoms that confers a particularchemical property on a biomolecule.furanose: A simple sugar containing thefive-membered furan ring.fusion protein: (DA family of proteinsthat facilitate membrane fusion.
(2) Theprotein product of a gene created by thefusion of two distinct genes.futile cycle: A set of enzyme-catalyzedcyclic reactions that results in release ofthermal energy by the hydrolysis of ATP.AG°': See standard free-energy change.gametes: Reproductive cells with a haploid gene content; sperm or egg cells.gangliosides: Sphingolipids, containingcomplex oligosaccharides as head groups;especially common in nervous tissue.gel filtration: A chromatographic procedure for the separation of a mixture ofmolecules on the basis of size; based onthe capacity of porous polymers to excludesolutes above a certain size.gene: A chromosomal segment that codesfor a single functional polypeptide chainor RNA molecule.gene expression: Transcription and, inthe case of proteins, translation to yieldthe product of a gene; a gene is expressedwhen its biological product is present andactive.gene splicing: The enzymatic attachmentof one gene, or part of a gene, to another.general acid—base catalysis: Catalysisinvolving proton transfers) to or from amolecule other than water.genetic code: The set of triplet codewords in DNA (or mRNA) coding for theamino acids of proteins.genetic information: The hereditary information contained in a sequence of nucleotide bases in chromosomal DNA orRNA.genetic map: A diagram showing the relative sequence and position of specificgenes along a chromosome.genome: All the genetic information encoded in a cell or virus.genotype: The genetic constitution of anorganism, as distinct from its physicalcharacteristics, or phenotype.geometric isomers: Isomers related byrotation about a double bond; also calledcis and trans isomers.germ-line cell: A type of animal cell thatis formed early in embryogenesis and maymultiply by mitosis or may produce, bymeiosis, cells that develop into gametes(egg or sperm cells).globular proteins: Soluble proteins witha globular (somewhat rounded) shape.glucogenic amino acids: Amino acidswith carbon chains that can be metabolically converted into glucose or glycogenvia gluconeogenesis.gluconeogenesis: The biosynthesis of acarbohydrate from simpler, noncarbohydrate precursors such as oxaloacetate orpyruvate.glycan: Another term for polysaccharide;a polymer of monosaccharide units joinedby glycosidic bonds.glycerophospholipid: An amphipathiclipid with a glycerol backbone; fatty acidsare ester-linked to C-l and C-2 of glycerol,and a polar alcohol is attached through aphosphodiester linkage to C-3.glycolipid: A lipid containing a carbohydrate group.glycolysis: The catabolic pathway bywhich a molecule of glucose is brokendown into two molecules of pyruvate.glycoprotein: A protein containing acarbohydrate group.glycosaminoglycan: A heteropolysaccharide of two alternating units: one iseither iV-acetylglucosamine or Af-acetylgalactosamine; the other is a uronic acid(usually glucuronic acid).
Formerly calledmucopolysaccharide.glycosidic bonds: Bonds between asugar and another molecule (typically analcohol, purine, pyrimidine, or sugar)through an intervening oxygen or nitrogenatom; the bonds are classified as O-glycosidic or iV-glycosidic, respectively.glyoxylate cycle: A variant of the citricacid cycle, for the net conversion of acetate into succinate and, eventually, newGlossarycarbohydrate; present in bacteria andsome plant cells.glyoxysome: A specialized peroxisomecontaining the enzymes of the glyoxylatecycle; found in cells of germinating seeds.Golgi complex: A complex membranousorganelle of eukaryotic cells; functions inthe posttranslational modification of proteins and their secretion from the cell orincorporation into the plasma membraneor organellar membranes.gram molecular weight: The weight ingrams of a compound that is numericallyequal to its molecular weight; the weightof 1 mole.grana: Stacks of thylakoids, flattenedmembranous sacs or discs, in chloroplasts.ground state: The normal, stable form ofan atom or molecule; as distinct from theexcited state.group transfer potential: A measure ofthe ability of a compound to donate anactivated group (such as a phosphate oracyl group); generally expressed as thestandard free energy of hydrolysis.half-life: The time required for the disappearance or decay of one-half of a givencomponent in a system.haploid: Having a single set of geneticinformation; describing a cell with onechromosome of each type.Haworth perspective formulas: Amethod for representing cyclic chemicalstructures so as to define the configuration of each substituent group; the methodcommonly used for representing sugars.helicase: An enzyme that catalyzes theseparation of strands in a DNA moleculebefore replication.helix, a: See a helix.heme: The iron-porphyrin prostheticgroup of heme proteins.heme protein: A protein containing aheme as a prosthetic group.hemoglobin: A heme protein in erythrocytes; functions in oxygen transport.Henderson-Hasselbalch equation: Anequation relating the pH, the pKa, and theratio of the concentrations of the protonacceptor (A") and proton-donor (HA) species in a solution.hepatocyte: The major cell type of livertissue.heteroduplex DNA: Duplex DNA containing complementary strands derivedfrom two different DNA molecules withsimilar sequences, often as a product ofgenetic recombination.heteropolysaccharide: A polysaccharidecontaining more than one type of sugar.heterotroph: An organism that requirescomplex nutrient molecules, such as glucose, as a source of energy and carbon.heterotropic enzyme: An allosteric enzyme requiring a modulator other than itssubstrate.hexose: A simple sugar with a backbonecontaining six carbon atoms.high-energy compound: A compoundthat on hydrolysis undergoes a large decrease in free energy under standard conditions.high-performance liquid chromatography (HPLC): Chromatographic procedures, often conducted at relatively highpressures, using automated equipmentthat permits refined and highly reproducible profiles.Hill reaction: The evolution of oxygenand the photoreduction of an artificialelectron acceptor by a chloroplast preparation in the absence of carbon dioxide.histones: The family of five basic proteins that associate tightly with DNA inthe chromosomes of all eukaryotic cells.Holliday intermediate: An intermediatein genetic recombination in which twodouble-stranded DNA molecules are joinedby virtue of a reciprocal crossover involving one strand of each molecule.holoenzyme: A catalytically active enzyme including all necessary subunits,prosthetic groups, and cofactors.homeobox: A conserved DNA sequence of180 base pairs encoding a protein domainfound in many proteins that play a regulatory role in development.homeodomain: The protein domain encoded by the homeobox.homeostasis: The maintenance of a dynamic steady state by regulatory mechanisms that compensate for changes in external circumstances.homeotic genes: Genes that regulate thedevelopment of the pattern of segments inthe Drosophila body plan; similar genesare found in most vertebrates.homologous genetic recombination:Recombination between two DNA molecules of similar sequence, occurring in allcells; occurs during meiosis and mitosis ineukaryotes.homologous proteins: Proteins havingsequences and functions similar in different species; for example, the hemoglobins.G-7homopolysaccharide: A polysaccharidemade up of only one type of monosaccharide unit.homotropic enzyme: An allosteric enzyme that uses its substrate as a modulator.hormone: A chemical substance synthesized in small amounts by an endocrinetissue and carried in the blood to anothertissue, where it acts as a messenger toregulate the function of the target tissueor organ.hormone receptor: A protein in, or onthe surface of, target cells that binds aspecific hormone and initiates the cellularresponse.hydrogen bond: A weak electrostatic attraction between one electronegative atom(such as oxygen or nitrogen) and a hydrogen atom covalently linked to a secondelectronegative atom.hydrolases: Enzymes (proteases, lipases,phosphatases, nucleases, for example) thatcatalyze hydrolysis reactions.hydrolysis: Cleavage of a bond, such asan anhydride or peptide bond, by the addition of the elements of water, yieldingtwo or more products.hydronium ion: The hydrated hydrogenion (H3O+).hydropathy index: A scale that expresses the relative hydrophobic and hydrophilic tendencies of a chemical group.hydrophilic: Polar or charged; describingmolecules or groups that associate with(dissolve easily in) water.hydrophobic: Nonpolar; describing molecules or groups that are insoluble inwater.hydrophobic interactions: The association of nonpolar groups, or compounds,with each other in aqueous systems,driven by the tendency of the surroundingwater molecules to seek their most stable(disordered) state.hyperchromic effect: The large increasein light absorption at 260 nm occurring asa double-helical DNA is melted (unwound).immune response: The capacity of a vertebrate to generate antibodies to an antigen, a macromolecule foreign to the organism.immunoglobulin: An antibody proteingenerated against, and capable of bindingspecifically to, an antigen.G-8Glossaryin vitro: "In glass"; that is, in the testtube.in vivo: "In life"; that is, in the living cellor organism.induced fit: A change in the conformation of an enzyme in response to substratebinding that renders the enzyme catalytically active; also used to denote changesin the conformation of any macromoleculein response to ligand binding such thatthe binding site of the macromolecule better conforms to the shape of the ligand.inducer: A signal molecule that, whenbound to a regulatory protein, producesan increase in the expression of a givengene.induction: An increase in the expressionof a gene in response to a change in theactivity of a regulatory protein.informational macromolecules: Biomolecules containing information in theform of specific sequences of differentmonomers; for example, many proteins,lipids, polysaccharides, and nucleic acids.initiation codon: AUG (sometimes GUGin prokaryotes); codes for the first aminoacid in a polypeptide sequence: iV-formylmethionine in prokaryotes, and methionine in eukaryotes.initiation complex: A complex of a ribosome with an mRNA and the initiatingMet-tRNAMet or fMet-tRNA™et, ready forthe elongation steps.inorganic pyrophosphatase: An enzymethat hydrolyzes a molecule of inorganicpyrophosphate to yield two molecules of(ortho) phosphate; also known as pyrophosphatase.insertion mutation: A mutation causedby insertion of one or more extra bases, ora mutagen, between two successive basesin DNA.insertion sequence: Specific base sequences at either end of a transposablesegment of DNA.integral membrane proteins: Proteinsfirmly bound to a membrane by hydrophobic interactions; as distinct from peripheral proteins.intercalating mutagen: A mutagen thatinserts itself between two successive basesin a nucleic acid, causing a frame-shiftmutation.intercalation: Insertion between twostacked aromatic or planar rings; for example, the insertion of a planar moleculebetween two successive bases in a nucleicacid.interferons: A class of glycoproteins withantiviral activities.intermediary metabolism: In cells, theenzyme-catalyzed reactions that extractchemical energy from nutrient moleculesand utilize it to synthesize and assemblecell components.intron (intervening sequence): A sequence of nucleotides in a gene that istranscribed but excised before the gene istranslated.ion channel: An integral membrane protein that provides for the regulated transport of a specific ion, or ions, across amembrane.ion-exchange resin: A polymeric resinthat contains fixed charged groups; usedin chromatographic columns to separateionic compounds.ion product of water (Kw): The productof the concentrations of H+ and OH" inpure water: Kw = [H+][OH'] = 1 x 10 1 4at 25 °C.ionizing radiation: A type of radiation,such as x rays, that causes loss of electrons from some organic molecules, thusmaking them more reactive.ionophore: A compound that binds oneor more metal ions and is capable of diffusing across a membrane, carrying thebound ion.iron-sulfur center: A prosthetic groupof certain redox proteins involved in electron transfers; Fe2+ or Fe3+ is bound toinorganic sulfur and to Cys groups in theprotein.isoelectric focusing: An electrophoreticmethod for separating macromolecules onthe basis of their isoelectric pH.isoelectric pH (isoelectric point): ThepH at which a solute has no net electriccharge and thus does not move in an electric field.isoenzymes: See isozymes.isomerases: Enzymes that catalyze thetransformation of compounds into theirpositional isomers.isomers: Any two molecules with thesame molecular formula but a differentarrangement of molecular groups.isoprene: The hydrocarbon 2-methyl-l,3butadiene, a recurring structural unit ofthe terpenoid biomolecules.isothermal: Occurring at constant temperature.isotopes: Stable or radioactive forms ofan element that differ in atomic weightbut are otherwise chemically identical tothe naturally abundant form of the element; used as tracers.isozymes: Multiple forms of an enzymethat catalyze the same reaction but differfrom each other in their amino acid se-quence, substrate affinity, VmaX5 and/orregulatory properties; also called isoenzymes.keratins: Insoluble protective or structural proteins consisting of parallel polypeptide chains in a-helical or /3 conformations.ketogenic amino acids: Amino acidswith carbon skeletons that can serve asprecursors of the ketone bodies.ketone bodies: Acetoacetate, D-/3hydroxybutyrate, and acetone; watersoluble fuels normally exported by theliver but overproduced during fasting orin untreated diabetes mellitus.ketose: A simple monosaccharide inwhich the carbonyl group is a ketone.ketosis: A condition in which the concentration of ketone bodies in the blood, tissues, and urine is abnormally high.kinases: Enzymes that catalyze the phosphorylation of certain molecules by ATP.kinetics: The study of reaction rates.Krebs cycle: See citric acid cycle.lagging strand: The DNA strand that,during replication, must be synthesized inthe direction opposite to that in which thereplication fork moves.law of mass action: The law stating thatthe rate of any given chemical reaction isproportional to the product of the activities (or concentrations) of the reactants.leader: A short sequence near the aminoterminus of a protein or the 5' end of anRNA that has a specialized targeting orregulatory function.leading strand: The DNA strand that,during replication, is synthesized in thesame direction in which the replicationfork moves.leaky mutant: A mutant gene that givesrise to a product with a detectable level ofbiological activity.leaving group: The departing or displaced molecular group in a unimolecularelimination or a bimolecular substitutionreaction.lethal mutation: A mutation that inactivates a biological function essential to thelife of the cell or organism.leucine zipper: A protein structuralGlossarymotif involved in protein-protein interactions in many eukaryotic regulatory proteins; consists of two interacting a helicesin which Leu residues in every seventhposition are a prominent feature of theinteracting surfaces.leukotrienes: A family of molecules derived from arachidonate; muscle contractants that constrict air passages in thelungs and are involved in asthma.levorotatory isomer: A stereoisomerthat rotates the plane of plane-polarizedlight counterclockwise.ligand: A small molecule that binds specifically to a larger one; for example, ahormone is the ligand for its specific protein receptor.light reactions: The reactions of photosynthesis that require light and cannotoccur in the dark; also known as thelight-dependent reactions.Lineweaver-Burk equation: An algebraic transform of the Michaelis-Mentenequation, allowing determination of Vmaxand Km by extrapolation of [S] to infinity.linking number: The number of timesone closed circular DNA strand is woundabout another; the number of topologicallinks holding the circles together.lipases: Enzymes that catalyze the hydrolysis of triacylglycerols.lipid: A small water-insoluble biomoleculegenerally containing fatty acids, sterols, orisoprenoid compounds.lipoate (lipoic acid): A vitamin for somemicroorganisms; an intermediate carrierof hydrogen atoms and acyl groups ina-keto acid dehydrogenases.lipoprotein: A lipid-protein aggregatethat serves to carry water-insoluble lipidsin the blood.
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