10 Генетическая инженерия (1160079), страница 14

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Alsocalled the phosphogluconate pathway.peptidase: An enzyme that hydrolyzes apeptide bond.peptide: Two or more amino acids covalently joined by peptide bonds.peptide bond: A substituted amide linkage between the a-amino group of oneamino acid and the a-carboxyl group ofanother, with the elimination of the elements of water.peptide mapping: The characteristictwo-dimensional pattern (on paper or gel)formed by the separation of a mixture ofpeptides resulting from partial hydrolysisof a protein; also known as peptide fingerprinting.peptidoglycan: A major component ofbacterial cell walls; generally consists ofparallel heteropolysaccharides cross-linkedby short peptides.peripheral proteins: Proteins that areloosely or reversibly bound to a membraneby hydrogen bonds or electrostatic forces;generally water-soluble once released fromthe membrane.permeases: See transporters.peroxisome: Membrane-bounded organelle in the cytoplasm of eukaryotic cells;contains peroxide-forming and peroxidedestroying enzymes.pH: The negative logarithm of the hydrogen ion concentration of an aqueous solution.phage: See bacteriophage.phenotype: The observable characteristics of an organism.phosphodiester linkage: A chemicalgrouping that contains two alcohols esterified to one molecule of phosphoric acid,which thus serves as a bridge betweenthem.phosphogluconate pathway: An oxidative pathway beginning with glucose-6phosphate and leading, via 6-phosphogluconate, to pentose phosphates and yielding NADPH.

Also called the pentosephosphate pathway.phospholipid: A lipid containing one ormore phosphate groups.phosphorolysis: Cleavage of a compoundwith phosphate as the attacking group;analogous to hydrolysis.phosphorylation: Formation of a phosphate derivative of a biomolecule, usuallyby enzymatic transfer of a phosphategroup from ATP.phosphorylation potential (AGp): Theactual free-energy change of ATP hydrolysis under the nonstandard conditions prevailing within a cell.photochemical reaction center: TheG-llpart of a photosynthetic complex wherethe energy of an absorbed photon causescharge separation, initiating electrontransfer*photon: The ultimate unit (a quantum) oflight energy.photophosphorylation: The enzymaticformation of ATP from ADP coupled to thelight-dependent transfer of electrons inphotosynthetic cells.photoreduction: The light-induced reduction of an electron acceptor in photosynthetic cells.photorespiration: Oxygen consumptionoccurring in illuminated temperate-zoneplants, largely due to oxidation of phosphoglycolate.photosynthesis: The use of light energyto produce carbohydrates from carbon dioxide and a reducing agent such as water.photosynthetic phosphorylation: Seephotophosphorylation.photosystem: In photosynthetic cells, afunctional set of light-absorbing pigmentsand its reaction center.phototroph: An organism that can usethe energy of light to synthesize its ownfuels from simple molecules such as carbon dioxide, oxygen, and water; as distinctfrom a chemotroph.pK: The negative logarithm of an equilibrium constant.plasma membrane: The exterior membrane surrounding the cytoplasm of a cell.plasma proteins: The proteins present inblood plasma.plasmalogen: A phospholipid with analkenyl ether substituent on the C-l ofglycerol.plasmid: An extrachromosomal, independently replicating, small circular DNAmolecule; commonly employed in geneticengineering.plastid: In plants, a self-replicating organelle; may differentiate into a chloroplast.platelets: Small, enucleated cells that initiate blood clotting; they arise from cellscalled megakaryocytes in the bone marrow.

Also known as thrombocytes.pleated sheet: The side-by-side, hydrogen-bonded arrangement of polypeptidechains in the extended /3 conformation.polar: Hydrophilic, or "water-loving"; describing molecules or groups that are soluble in water.polarity: (1) In chemistry, the nonuniformdistribution of electrons in a molecule;polar molecules are usually soluble inG-12Glossarywater. (2) In molecular biology, the distinction between the 5' and 3' ends ofnucleic acids.polyclonal antibodies: A heterogeneouspool of antibodies produced in an animalby a number of different B lymphocytes inresponse to an antigen. Different antibodies in the pool recognize different parts ofthe antigen.polylinker: A short, often synthetic, fragment of DNA containing recognition sequences for several restriction endonucleases.polymerase chain reaction (PCR): Arepetitive procedure that results in a geometric amplification of a specific DNAsequence.polymorphic: Describing a protein forwhich amino acid sequence variants existin a population of organisms, but the variations do not destroy the protein's function.polynucleotide: A covalently linked sequence of nucleotides in which the 3' hydroxyl of the pentose of one nucleotideresidue is joined by a phosphodiester bondto the 5' hydroxyl of the pentose of thenext residue.polypeptide: A long chain of amino acidslinked by peptide bonds; the molecularweight is generally less than 10,000.polyribosome: See polysome.polysaccharide: A linear or branchedpolymer of monosaccharide units linkedby glycosidic bonds.polysome (polyribosome): A complex ofan mRNA molecule and two or more ribosomes.porphyrin: Complex nitrogenous compound containing four substituted pyrrolescovalently joined into a ring; often complexed with a central metal atom.positive cooperativity: A phenomenonof some multisubunit enzymes or proteinsin which binding of a ligand or substrateto one subunit facilitates binding to another subunit.posttranscriptional processing: Theenzymatic processing of the primary RNAtranscript, producing functional mRNA,tRNA, and/or rRNA molecules.posttranslational modification: Enzymatic processing of a polypeptide chainafter translation from its mRNA.primary structure: A description of thecovalent backbone of a polymer (macromolecule), including the sequence of monomeric subunits and any interchain andintrachain covalent bonds.primary transcript: The immediateRNA product of transcription before anyposttranscriptional processing reactions.primase: An enzyme that catalyzes theformation of RNA oligonucleotides used asprimers by DNA polymerases.primer: A short oligomer (of sugars ornucleotides, for example) to which an enzyme adds additional monomeric subunits.probe: A labeled fragment of nucleic acidcontaining a nucleotide sequence complementary to a gene or genomic sequencethat one wishes to detect in a hybridization experiment.processivity: For any enzyme that catalyzes the synthesis of a biological polymer,the property of adding multiple subunitsto the polymer without dissociating fromthe substrate.prochiral molecule: A symmetric molecule that can react asymmetrically withan enzyme having an asymmetric activesite, generating a chiral product.projection formulas: A method for representing molecules to show the configuration of groups around chiral centers; alsoknown as Fischer projection formulas.prokaryote: A bacterium; a unicellularorganism with a single chromosome, nonuclear envelope, and no membranebounded organelles.promoter: A DNA sequence at whichRNA polymerase may bind, leading to initiation of transcription.prophage: A bacteriophage in an inactivestate in which the genome is either integrated into the chromosome of the hostcell or (sometimes) replicated autonomously.prostaglandins: A class of lipid-soluble,hormonelike regulatory molecules derivedfrom arachidonate and other polyunsaturated fatty acids.prosthetic group: A metal ion or an organic compound (other than an aminoacid) that is covalently bound to a proteinand is essential to its activity.protein: A macromolecule composed ofone or more polypeptide chains, each witha characteristic sequence of amino acidslinked by peptide bonds.protein kinases: Enzymes that phosphorylate certain amino acid residues in specific proteins.protein targeting: The process by whichnewly synthesized proteins are sorted andtransported to their proper locations inthe cell.proteoglycan: A hybrid macromoleculeconsisting of a heteropolysaccharide joinedto a polypeptide; the polysaccharide is themajor component.proto-oncogene: A cellular gene, usuallyencoding a regulatory protein, that can beconverted into an oncogene by mutation.proton acceptor: An anionic compoundcapable of accepting a proton from a proton donor; that is, a base.proton donor: The donor of a proton inan acid—base reaction; that is, an acid.proton-motive force: The electrochemical potential inherent in a transmembranegradient of H+ concentration; used in oxidative phosphorylation and photophosphorylation to drive ATP synthesis.protoplasm: A general term referring tothe entire contents of a living cell.purine: A nitrogenous heterocyclic basefound in nucleotides and nucleic acids;containing fused pyrimidine and imidazolerings.puromycin: An antibiotic that inhibitspolypeptide synthesis by being incorporated into a growing polypeptide chain,causing its premature termination.pyranose: A simple sugar containing thesix-membered pyran ring.pyridine nucleotide: A nucleotide coenzyme containing the pyridine derivativenicotinamide; NAD or NADP.pyridoxal phosphate: A coenzyme containing the vitamin pyridoxine (vitaminB6); functions in reactions involving aminogroup transfer.pyrimidine: A nitrogenous heterocyclicbase found in nucleotides and nucleicacids.pyrimidine dimer: A covalently joineddimer of two adjacent pyrimidine residuesin DNA, induced by absorption of UVlight; most commonly derived from twoadjacent thymines (a thymine dimer).pyrophosphatase: See inorganic pyrophosphatase.quantum: The ultimate unit of energy.quaternary structure: The three-dimensional structure of a multisubunit protein;particularly the manner in which the subunits fit together.R group: (1) Formally, an abbreviationdenoting any alkyl group.

(2) Occasionally,used in a more general sense to denotevirtually any organic substituent (the Rgroups of amino acids, for example).racemic mixture (racemate): An equimolar mixture of the D and L stereoisomers of an optically active compound.Glossaryradical: An atom or group of atoms possessing an unpaired electron; also called afree radical.radioactive isotope: An isotopic form ofan element with an unstable nucleus thatstabilizes itself by emitting ionizing radiation.radioimmunoassay: A sensitive andquantitative method for detecting traceamounts of a biomolecule, based on itscapacity to displace a radioactive form ofthe molecule from combination with itsspecific antibody.rate-limiting step: (1) Generally, thestep in an enzymatic reaction with thegreatest activation energy or the transition state of highest free energy. (2) Theslowest step in a metabolic pathway.reaction intermediate: Any chemicalspecies in a reaction pathway that has afinite chemical lifetime.reading frame: A contiguous and nonoverlapping set of three-nucleotide codonsin DNA or RNA.recombinant DNA: DNA formed by thejoining of genes into new combinations.redox pair: An electron donor and itscorresponding oxidized form; for example,NADH and NAD\redox reaction: See oxidation-reductionreaction.reducing agent (reductant): The electron donor in an oxidation-reduction reaction.reducing end: The end of a polysaccharide having a terminal sugar with a freeanomeric carbon; the terminal residue canact as a reducing sugar.reducing equivalent: A general or neutral term for an electron or an electronequivalent in the form of a hydrogen atomor a hydride ion.reducing sugar: A sugar in which thecarbonyl (anomeric) carbon is not involvedin a glycosidic bond and can thereforeundergo oxidation.reduction: The gain of electrons by acompound or ion.regulatory enzyme: An enzyme having aregulatory function through its capacity toundergo a change in catalytic activity byallosteric mechanisms or by covalent modification.regulatory gene: A gene that gives riseto a product involved in the regulation ofthe expression of another gene; for example, a gene coding for a repressor protein.regulatory sequence: A DNA sequenceinvolved in regulating the expression of agene; for example, a promoter or operator.regulon: A group of genes or operonsthat are coordinately regulated eventhough some, or all, may be spatially distant within the chromosome or genome.release factors: See termination factors.releasing factors: Hypothalamic hormones that stimulate release of other hormones by the pituitary gland.renaturation: Refolding of an unfolded(denatured) globular protein so as to restore native structure and protein function.replication: Synthesis of a daughter duplex DNA molecule identical to the parental duplex DNA.replisome: The multiprotein complexthat promotes DNA synthesis at the replication fork.repressible enzyme: In bacteria, an enzyme whose synthesis is inhibited whenits reaction product is readily available tothe cell.repression: A decrease in the expressionof a gene in response to a change in theactivity of a regulatory protein.repressor: The protein that binds to theregulatory sequence or operator for agene, blocking its transcription.residue: A single unit within a polymer;for example, an amino acid within a polypeptide chain.

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