10 Генетическая инженерия (1160079), страница 15
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The term reflects the factthat sugars, nucleotides, and amino acidslose a few atoms (generally the elementsof water) when incorporated in their respective polymers.respiration: The catabolic process inwhich electrons are removed from nutrient molecules and passed through a chainof carriers to oxygen.respiratory chain: The electron transferchain; a sequence of electron-carrying proteins that transfer electrons from substrates to molecular oxygen in aerobiccells.restriction endonucleases: Site-specificendodeoxyribonucleases causing cleavageof both strands of DNA at points withinor near the specific site recognized by theenzyme; important tools in genetic engineering.restriction fragment: A segment ofdouble-stranded DNA produced by theaction of a restriction endonuclease on alarger DNA.restriction fragment length polymorphisms (RFLPs): Variations, among individuals in a population, in the length ofcertain restriction fragments within whichcertain genomic sequences occur.
Thesevariations result from rare sequencechanges that create or destroy restrictionsites in the genome.G-13retrovirus: An RNA virus containing areverse transcriptase.reverse transcriptase: An RNA-directedDNA polymer ase in retro viruses; capableof making DNA complementary to anRNA.ribonuclease: A nuclease that catalyzesthe hydrolysis of certain internucleotidelinkages of RNA.ribonucleic acid: See RNA.ribonucleotide: A nucleotide containingD-ribose as its pentose component.ribosomal RNA (rRNA): A class of RNAmolecules serving as components of ribosomes.ribosome: A supramolecular complex ofrRNAs and proteins, approximately 18 to22 nm in diameter; the site of proteinsynthesis.Nribozymes: Ribonucleic acid moleculeswith catalytic activities; RNA enzymes.RNA (ribonucleic acid): A polyribonucleotide of a specific sequence linked bysuccessive 3',5'-phosphodiester bonds.RNA polymerase: An enzyme that catalyzes the formation of RNA from ribonucleoside 5'-triphosphates, using a strandof DNA or RNA as a template.RNA splicing: Removal of introns andjoining of exons in a primary transcript.rRNA: See ribosomal RNA.S-adenosylmethionine (adoMet): Anenzymatic cofactor involved in methylgroup transfers.salvage pathway: Synthesis of a biomolecule, such as a nucleotide, from intermediates in the degradative pathway for thebiomolecule; a recycling pathway, as distinct from a de novo pathway.saponification: Alkaline hydrolysis oftriacylglycerols to yield fatty acids assoaps.sarcomere: A functional and structuralunit of the muscle contractile system.satellite DNA: Highly repeated, nontranslated segments of DNA in eukaryoticchromosomes; most often associated withthe centromeric region.
Its function is notclear.saturated fatty acid: A fatty acid containing a fully saturated alkyl chain.second law of thermodynamics: Thelaw stating that in any chemical or physical process, the entropy of the universetends to increase.G-14Glossarysecond messenger: An effector moleculesynthesized within a cell in response toan external signal (first messenger) suchas a hormone.secondary metabolism: Pathways thatlead to specialized products not found inevery living cell.secondary structure: The residue-byresidue conformation of the backbone of apolymer.sedimentation coefficient: A physicalconstant specifying the rate of sedimentation of a particle in a centrifugal fieldunder specified conditions.Shine-Dalgarno sequence: A sequencein an mRNA required for binding prokaryotic ribosomes.shuttle vector: A recombinant DNA vector that can be replicated in two or moredifferent host species.
See also vector.sickle-cell anemia: A human diseasecharacterized by defective hemoglobinmolecules; caused by a homozygous allelecoding for the /3 chain of hemoglobin.sickle-cell trait: A human condition recognized by the sickling of erythrocyteswhen exposed to low oxygen tension; occurs in individuals heterozygous for theallele responsible for sickle-cell anemia.signal sequence: An amino-terminal sequence that signals the cellular fate ordestination of a newly synthesized protein.signal transduction: The process bywhich an extracellular signal (chemical,mechanical, or electrical) is amplified andconverted to a cellular response.silent mutation: A mutation in a genethat causes no detectable change in thebiological characteristics of the gene product.simple diffusion: The movement of solute molecules across a membrane to aregion of lower concentration, unassistedby a protein transporter.simple protein: A protein yielding onlyamino acids on hydrolysis.site-directed mutagenesis: A set ofmethods used to create specific alterationsin the sequence of a gene.site-specific recombination: A type ofgenetic recombination that occurs only atspecific sequences.small nuclear RNA (snRNA): Any ofseveral small RNA molecules in the nucleus; most have a role in the splicing reactions that remove introns from mRNA,tRNA, and rRNA molecules.somatic cells: All body cells except thegerm-line cells.SOS response: In bacteria, a coordinatedinduction of a variety of genes as a response to high levels of DNA damage.Southern blot: A DNA hybridization procedure in which one or more specific DNAfragments are detected in a larger population by means of hybridization to a complementary, labeled nucleic acid probe.specific activity: The number of micromoles (fjunol) of a substrate transformedby an enzyme preparation per minute permilligram of protein at 25 °C; a measureof enzyme purity.specific heat: The amount of energy (injoules or calories) needed to raise the temperature of 1 g of a pure substance by1°C.specific rotation: The rotation, in degrees, of the plane of plane-polarized light(D-line of sodium) by an optically activecompound at 25 °C, with a specified concentration and light path.specificity: The ability of an enzyme orreceptor to discriminate among competingsubstrates or ligands.sphingolipid: An amphipathic lipid witha sphingosine backbone to which are attached a long-chain fatty acid and a polaralcohol.splicing: See gene splicing; RNA splicing.standard free-energy change (AG°):The free-energy change for a reaction occurring under a set of standard conditions: temperature, 298 K; pressure, 1 atmor 101.3 kPa; and all solutes at 1 M concentration.
AG°' denotes the standardfree-energy change at pH 7.0.standard reduction potential (E0')iThe electromotive force exhibited at anelectrode by 1 M concentrations of a reducing agent and its oxidized form at 25 °Cand pH 7.0; a measure of the relative tendency of the reducing agent to lose electrons.steady state: A nonequilibrium state of asystem through which matter is flowingand in which all components remain at aconstant concentration.stem cells: The common, self-regenerating cells in bone marrow that give rise todifferentiated blood cells such as erythrocytes and lymphocytes.stereoisomers: Compounds that have thesame composition and the same order ofatomic connections, but different molecular arrangements.sterols: A class of lipids containing thesteroid nucleus.sticky ends: Two DNA ends in the sameDNA molecule, or in different molecules,with short overhanging single-strandedsegments that are complementary to oneanother, facilitating ligation of the ends;also known as cohesive ends.stop codons: See termination codons.stroma: The space and aqueous solutionenclosed within the inner membrane of achloroplast, not including the contentswithin the thylakoid membranes.structural gene: A gene coding for a protein or RNA molecule; as distinct from aregulatory gene.substitution mutation: A mutationcaused by the replacement of one base byanother.substrate: The specific compound actedupon by an enzyme.substrate-level phosphorylation: Phosphorylation of ADP or some other nucleoside 5'-diphosphate coupled to the dehydrogenation of an organic substrate;independent of the electron transfer chain.suicide inhibitor: A relatively inert molecule that is transformed by an enzyme,at its active site, into a reactive substancethat irreversibly inactivates the enzyme.suppressor mutation: A mutation thattotally or partially restores a function lostby a primary mutation; located at a sitedifferent from the site of the primarymutation.Svedberg (S): A unit of measure of therate at which a particle sediments in acentrifugal field.symbionts: Two or more organisms thatare mutually interdependent; usually living in physical association.symport: Cotransport of solutes across amembrane in the same direction.synthases: Enzymes that catalyze condensation reactions in which no nucleoside triphosphate is required as an energysource.synthetases: Enzymes that catalyze condensation reactions using ATP or anothernucleoside triphosphate as an energysource.system: An isolated collection of matter;all other matter in the universe apartfrom the system is called the surroundings.iftelomere: Specialized nucleic acid structure found at the ends of linear eukaryotic chromosomes.temperate phage: A phage whose DNAmay be incorporated into the host-cellGlossarygenome without being expressed; as distinct from a virulent phage, which destroys the host cell.template: A macromolecular mold or pattern for the synthesis of an informationalmacromolecule.terminal transferase: An enzyme thatcatalyzes the addition of nucleotide residues of a single kind to the 3' end of DNAchains.termination codons: UAA, UAG, andUGA; in protein synthesis, signal the termination of a polypeptide chain.
Alsoknown as stop codons.termination factors: Protein factors ofthe cytosol required in releasing a completed polypeptide chain from a ribosome;also known as release factors.termination sequence: A DNA sequencethat appears at the end of a transcriptional unit and signals the end of transcription.terpenes: Organic hydrocarbons or hydrocarbon derivatives constructed from recurring isoprene units.
They produce some ofthe scents and tastes of plant products;for example, the scents of geranium leavesand pine needles.tertiary structure: The three-dimensional conformation of a polymer in itsnative folded state.tetrahydrobiopterin: The reduced coenzyme form of biopterin.tetrahydrofolate: The reduced, activecoenzyme form of the vitamin folate.thiamine pyrophosphate: The activecoenzyme form of vitamin B^ involved inaldehyde transfer reactions.thioester: An ester of a carboxylic acidwith a thiol or mercaptan.3' end: The end of a nucleic acid thatlacks a nucleotide bound at the 3' positionof the terminal residue.thrombocytes: See platelets.thromboxanes: A class of molecules derived from arachidonate and involved inplatelet aggregation during blood clotting.thylakoid: Closed cisterna, or disc,formed by the pigment-bearing internalmembranes of chloroplasts.thymine dimer: See pyrimidine dimer.tissue culture: Method by which cellsderived from multicellular organisms aregrown in liquid media.titration curve: A plot of the pH versusthe equivalents of base added during titration of an acid.tocopherols: Forms of vitamin E.topoisomerases: Enzymes that introducepositive or negative supercoils in closed,circular duplex DNA.topoisomers: Different forms of a covalently closed, circular DNA molecule thatdiffer only in their linking number.toxins: Proteins produced by some organisms and toxic to certain other species.trace element: A chemical element required by an organism in only traceamounts.transaminases: See aminotransferases.transamination: Enzymatic transfer ofan amino group from an a-amino acid toan a-keto acid.transcription: The enzymatic processwhereby the genetic information containedin one strand of DNA is used to specify acomplementary sequence of bases in anmRNA chain.transcriptional control: The regulationof a protein's synthesis by regulation ofthe formation of its mRNA.transduction: (1) Generally, the conversion of energy or information from oneform to another.
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