中科院分子生物学试题库题库4.doc

GLOSSARYAbundance of an mRNA is the average number of molecules per cell.Abundant mRNAs consist of a small number of individual species, each present in a large number of copies per cell.Acceptor splicing sitesee right splicing junction.Acentric fragment of a chromosome (generated by breakage) lacks a centromere and is lost cell division.Acrocentric chromosome has the centromere located nearer one end than the other.Active site is the restricted part of a protein to which a substrate binds.Allele is one of several alternative forms of a gene occupying a given locus on a chromosome.Allelic exclusion describes the expression in any particular lymphocyte of only one allele coding for the expressed immunoglobulin.Allosteric control refers to the ability of an interaction at one site of a protein to influence the activity of another site.Alu family is a set of dispersed, related sequences, each300 bp long, in the human genome. The individual members have Alu cleavage sites at each end (hence the name).Alu-equivalent family is the set of sequences in a mammalian genome that is related to the human Alu family.-Amanitin is a bicyclic octapeptide derived from the poisonous mushroom Amanita phalloides; it inhibhits transcription by certain eukaryotic RNA polymerases, especially RNA polymerase II.Amber codon is the nucleotide triplet UAG, one of three codons that cause termination of protein synthesis.Amber mutaion describes any change in DNA that creates an amber codon at a site previously occupied by a codon representing an amino acid in a protein.Amber suppressors are mutant genes that code for tRNAs whose anticodons have been altered so that they can respond to UAG codons as well as or instead of to their previous codons.Aminoacyl-tRNA is transfer RNA carrying an amino acid; the covalent linkage is between the NH2 group of the amino acid and either the 3-or-2-OH group of the terminal base of the tRNA.Aminoacyl-tRNA synthetases are enzymes responsible for covalently linking amino acids to the 2 or 3-OH position of tRNA.Amphipathic structures have two surfaces, one hydrophilic and one hydrophobic. Lipids are amphipathic; and some protein regions may form amphipathic; and some protein regions may form amphipathic helices, with one charged face and one neutral face.Amplification refers to the production of additional copies of a chromosomal sequence, found as intrachromosomal or extrachromoxomal DNA.Anchorage dependence describes the need of normal eukaryotic cells for a surface to attach to in order to grow in culture.Aneuploid chromosome constitution differes from the usal diploid constitution by loss or duplication of chromosomes or chromosomal segments. Annealing is the pairing of complementary single strands of DNA to form a double helix.Antibody is a protein (immunoglobulin) produced by B lymphocyte cells that recognizes a particular foreign antigen,and thusw triggers the immune response. Anticoding strand of duples DNA is used as a template to direct the synthesis of RNA that is complementary to it.Antigen is any molecule whose entry into an organism provokes synthesis of an antibody (immunoglobulin).Antiparallel strands of the double helix are organized in opposite orientation, so that the 5 end of one strand is aligened with the 3 end of the other strand.Antitermination proteins allow RNA polymerase to transcribe through certain terminator sites.Ap endonucleases make incisions in DNA on the 5 side of either apurinic or apyrimidinc sites.Apoinducer is a protein that binds to DNA to switch on transcription by RNA polymerase.Archebacteria comprise a minor line of prokaryotes, and may have introns in the genome. Ascus of a fungus contains a tetrad or octad of the (haploid) spores, representhing the products of a sihngle meiosis. att sties are the loci on a phage and the bacterial chromosome at which recombination integrates the phage into. or excises it from , the bacterial chromosome.Attenuation describes the regulation of termination of transcription that is involved in controlling the expression of some bacterial operons.Attenuator is the terminator sequence at which attenuatioj occurs. Autogenous conhtrol describes the action of a gene product that either inhibits (negative autogenous control) or activates (positive autogenous control) expression of the gene coding for it.Autonomous controlling element in maize is an active transposon with the ability to transpose (cf nonautonomous controlling element).Autoradiography detects radioactively labeled molecules by their effect in creating an image on pholtographic film.Autosomes are all the chromosomes except the sex chromosomes; a diploid cell has two copies of each autosome.Blymphocytes (or B cells) are the cells responsible for synthesizing antibodies.Backcross is another (earlier) term for a testcross.Back mutation reverses the effect of a mutation that hand inactivated a gene; thus it restores wild type.Bacteriophages are viruses that infect bacteria; often abbreviated as phages.Balbaini ring is an extremely large puff at a band of a polytene chromosome.Bands of polytene chromosomes are visible as dense regions that contain the majority of DNA;bands of normal chromosomes are relatively much larger and are generated in the form of regions that retain a stain on certain chemical treatments.Base pair (bp) is a partnership of A with T or of C with G in a DNA double helix; other pairs can be formed in RNA under certain circumstances.Bidirectional replication is accomplished when two replication forks move away from the same origin in different directions.Bivalent is the structure containing all four chromatids (two representing each homologue) at the start of meiosis.Blastoderm is a stage of insect embryogenesis in which a layer of nuclei or cells around the embryo surround an internal mass of yolk.Blocked reading frame cannot be translated into protein because it is interrupted by termination codons.Blunt-end ligation is a reaction that joins two DNA duplex molecules directly at their ends.bp is an abbreviation for base pairs; distance along DNA is measured in bp.Branch migration describes the ability of a DNA strand partially paired with its complement in a duplex to extend its pairing by displacing the resident strand with which it is homologous.Breackage and reunion describes the mode of genetic recombination, in which two DNA duplex molecules are broken at corresponding points and then rejoined crosswise (involving formation of a length of heteroduplex DNA around the site of joining).Buoyant desity measures the ability of a substance to float in some standard fluid, for example, CsCl.C banding is a technique for generating stained regions around centromeres.C genes code for the constant regions of immunoglobulin protein chains.C value is the total amount of DNA in a haploid genome.CAAT box is part of a conserved sequence located upstream of the startpoints of eukaryotic transcription units; it is recognized by a large group of transcription factors.Cap is the structure at the 5 end of eukaryotic mRNA, introduced after transcripton by linking the terminal phosphate of 5 GTP to the terminal base of the mRNA. The added G (and sometimes some other bases) are methylated, giving a structure of the form 7MeG5ppp 5NpCAP(CRP) is a positive regulator protein activated by cyclic AMP. It is needed for RNA polymerase to initiate transcription of certain (catabolitesensitive) operons of E. coli.Capsid is the external protein coat of a virus particle.Catabolite repression describes the decreased expression of many bacterial operons that results from addition of glucose. It is caused by a decrease in the level of cyclic AMP, which in turn inactivates the CAP regulator.cDNA is a single-stranded DNA complementary to an RNA, synthesized from it by reverse transcription in vitro.cDNA clone is a duplex DNA sequence representing an RNA, carried in a cloning vector.Cell cycle is the period from one division to the next.Cell hybrid is a somatic cell containing chromosomes derived from parental cells of different species (e.g. a man-mouse somatic cell hybrid), generating by fusing the cells to form a heterokaryon in which the nuclei subsequently fused.Centrioles are small hollow cylinders consisting of microtubules that become located near the poles during mitosis. They reside within the centrosomes.Centromere is a constricted region of a chromosome that includes the site of attachment to the mitotic or meiotic spindle (see also kinetochore).Centrosomes are the regions from which microtubules are organized at the poles of a mitotic cell. In animal cells, each centrosome contains a pair of centrioles surrounded by a dense amorphous region to which the microtubules attach. See also MTOC.Molecular chaperone is a protein that is needed for the assembly or proper folding of some other protein, but which is not itself a component of the target complex.Chemical complexity is the amount of a DNA component measured by chemical assay.Chi sequence is an octamer that provides a hotspot for RecA-mediated genetic recombination in E. coli.Chi structure is a joint between two duplex molecules of DNA revealed by cleaving an intermediate of two joined circles to generate linear ends in each circle. It resembles a Greek chi in outline, hence the name.Chiasma (pl. chiasmata) is a site at which two homologous chromosomes appear to have exchanged material during meiosis.Chromatids are the copies of a chromosome produced by replication. The name is usually used to describe them in the period before they separate at the subsequent cell division.Chromatin is the complex of DNA and protein in the nucleus of the interphase cell. Individual chromosomes cannot be distinguished in it .It was originally recognized by its reaction with stains specific for DNA.Chromocenter is an aggregate of heterochromatin from different chromosomes.Chromomeres are densely staining granules visible in chromosomes under certain conditions, especially early in meiosis, when a chromosome may appear to consist of a series of chromomeres.Chromosome is a discrete unit of the genome carrying many genes. Each chromosome counsists of a very long molecule of duplex DNA and an approximately equal mass of proteins. It is visible as a morphological entity only during cell division.Chromosome walking describes the sequential isolation of clones carrying overlapping sequences of DNA, allowing large regions of the chromosome to be spanned. Walking is often performed in order to reach a particular locus of interest.cis-acting locus affects the activity only of DNA sequences on its own molecule of DNA; this property usually implies that the locus does not code for protein.cis-acting protein has the exceptional property of acting only on the molecule of DNA from which it was expressed.cis configuration describes two sites on the same molecule of DNA.cis/trans test assays the effect of relative configuration on expression of two mutations. In a double heterozygote, two mutations in the same gene show mutant phenotype in trans configuration, wild-type in cis configuration.Cistron is the geneti unit defined by the cis/trans test; equivalent to gene ib comprising a unit of DNA representing a protein.Class switching is a change in the expression of the c cregion of an immunoglobulin heavy chain during lymphocyte differentiation.Clone describes a large number of cells or molecules identical with a single ancestral cell or molecule.Cloning vector is a plasmid or phage that is used to carry inserted foreign DNA for the purposes of producing more material or a protein product.Closed reading frame contains termination codons that prevent its translation into protein.Coated vesicles are vesicles whose membrane has on its surface a layer of the protein clathrin.Coconversion is the simultaneous correction of two sites during gene conversion.Coding strand of DNA has the same sequence as mRNA.Codominant alleles both contribute to the phenotype; neither is dominant over the other.Coevolution see concerted evolution.Cognate tRNAs are those recognized by a particular aminoacy-tRNA synthetase.Coointegrate structure is produced by fusion of two replicons, one originally possessing a transposon, the other lacking it; the cointegrate has copies of the transposon present at both junctions of the replicons, oriented as directrepeats.Cold-sensitive mutant is defective at low temperature but functional at normal temlperature.Colony hybridization is a technique for using in situ hybridization to identify bacteria carrying chimeric vectors whose inserted DNA is homologous with some particular sequence.Compatibility group of plasmids contains members unable to coexist in the same bacterial cell.Complementation refers to the ability of independent (nonallelic)genes to provide diffusible products that produce wild phenotype when two mutants are tested in trans configuration in a heterozygote.In vitro complementation assay consists of identifying a component of a wid-type cell that can confer activity on an extract prepared from a mutant cell. The assay identifies the component rendered inactive by the mutation.Complementation group is a series of mutations unable to complement when tested in pairwise combinations in trans; defines a genetic unit (the cistron) that might better be called a noncomplex mentation group.Complex locus (of D. melanogaster) has genetic properties inconsistent with the function of a gene representing a single protein. Complex loci are usually very large (100kb) at the molecular level. Complexity is the total length of different sequences of DNA present in a given preparation. Compostie transposons have a central region flanked on each side by insertion sequences, either or both of which may enable the entire element to transpose.Concatemer of DNA consists of a series of unit genomes repeated in tandem.Concatenated circles of DNA are interlocked like rings one a chain.Concerted evolution describes the ability of two related genes to evolve together as though constituting a single locus.Condensation reaction is one in which a covalent bond is formed with loss of a water molecule, as in the addition of an amino acid to a polypeptide chain.Conditional lethal mlutations kill a cell or virus under certain (nonpermissive) conditions, but allow it to survive under other (permissive) conditions.Conjugation describes mathing between two bacterial cells, when (part of ) the chromosome is transferred from one to the other.Consensus sequence is an idealized sequence in which each position represents the base most often found when many actual sequences are compared.Conservative recombination involves breakage and reunion of preexisting strands of DNA without any synthesis of new stretches of DNA.Conservative transposition refers to the movement of large elements, originally classified as transposons, but now considered to be episomes. The mechanism of movement resembles that of phage lambda.Constant regions of immunoglobulins are coded by C genes and are the parts of the chain that vary least. Those of heavy chains identify the type of immunoglobulin.Constitutive genes are expressed as a function of the interaction of RNA polymerase with the promoter, without additional regulation; sometimes also called household genes in the context of describing functions expressed in all cells at a low level.Constitutive heterochromatin describes the inert state of permanently nonexpressed sequences, usually satellite DNA.Constitutive mutations cause genes that usually are regulated to be expressed without regulation.Contractile ring is a ring of actin filaments that forms around the equator at the end of mitosis and is responsible for pinching the daughter cells apart.Controlling elements of maize are transposable units originally identified solely by their genetic properties. They may be autonomous (able to transpose independently) or nonautonomous (able to element).Coordinate regulation refers to the common control of a group of genes.Cordycepin is 3 deoxyadenosine, an inhibitor of polyadenylation of RNA.Core DNA is the 14.6 bp of DNA contained on a core particle.Core particle is a digestion product of the nucleosome that retains the histone octamer and has 14.6 bp of DNA; its structure appears similar to that of the nucleosome itself.Corepressor is a small molecule that triggers repression of transcription by binding to a regulator protein.Cosmids are plasmids into which phage lambda cos sites have been inserted; as a result, the plasmid DNA can be packaged in vitro in the phage coat.Cot is the product of DNA concentration and time of incubation in a reassociation reaction.Cot is the Cot required to proceed to half completion of the reaction; it is directly proportional to the unique length of reassociating DNA.Cotransfection is the simultaneous transfection of two markers.Crossing-over describes the reciprocal exchange of material between chromosomes that occurs during meiosis and is responsible for genetic recombination.Crossover fixation refers to a possible consequence of unequal crossing-over that allows a mutation in one member of a tandem cluster to spread through the whole cluster (or to be eliminated).Cruciform is the structure produced at inverted repeats of DNA if the repeated sequence pairs with its complement on the same strand (instead of with its regular partner in the other strand of the duplex).Cryptic satellite is a satellite DNA sequence not identified as such by a separate peak on a density gradient; that is, it remains present in main-band DNA.ctDNA is chloroplast DNA.Cyclic AMP (cAMP) is a molecule of AMP in wh