考题二.docx

1、考题二Stem is the base-paired segment of a hairpin.Sticky ends are complementary single strands of DNA that protrude from opposite ends of a duplex or from ends of different duplex molecules; can be generated by staggered cuts in duplex DNA.Stop codons are the three triplets (UAA, UAG, UGA) which termi

2、nate protein synthesis.Strand displacement is a mode of replication of some viruses in which a new DNA strand grows by displacing the previous (homologous) strand of the duplex.Streptolydigins inhibit the elongation of transcription by bacterial RNA polymerase.Stingent replication describes the limi

3、tation of single-copy plasmids to replication pari passu with the bacterial chromosome.Stringent response refers to the ability of a bacterium to shut down synthesis of tRNA and rigosomes in a poor-growth medium.Structural gene codes for any RNA or protein product other than a regulator.Supercoiling

4、 dexcribes the coiling of a closed duplex DNA in space so that it crosses over its own axis.Superrepressed means the same as uninducible.Suppression describes the occurrence of changes that eliminate the effects of a mutation without reversing the original change in DNA.Suppressor (extragenic) is us

5、ually a gene coding a mutant tRNA that reads the mutated codon eigher in the sense of the original condon or to give an acceptable substitute for the original meaning.Suppressor (intragenic) is a compensating mutation that restores the original reading frame after a frameshift.Synapsis describes the

6、 association of the two pairs of sister chromatids representing homologous chromosomes that occurs at the start of meiosis; resulting structure is called a bivalent.Synaptonemal complex describes the morphological structure of synapsed chromosomes.Syntenic genetic loci lie on the same chromosome.T C

7、ells are lymphocytes of the T (thymic) lineage; may be subdivived into several functional types. They carry TcR (T cell receptor) and are involved in the cell-mediated immune response.Tm is the abbreviation for melting temperature.Tandem repeats are multiple copies of the same sequence lying in seri

8、es.TATA box is a conserved AT-rich septamer found about 25 bp bdfore the startpoint of each eukaryotic RNA polymerase II transcription unit; may be involved in positioning the enzyme for correct intitiation.Telomerase is the ribonucleoprotein enzyme that creates repeating units of one strand at the

9、telomere, by adding individual bases.Telomere is the natural end of a chromosome; the DNA sequence consists of a simple repeating unit with a protruding single-stranded end that may fold into a hairpin.Temperature-sensitive mutation creates a gene product that is functional at low temperature but in

10、active at higher temperature (the reverse relationship is usually called cold- sensitive).Termainal redundancy describes the repetition of the same sequence at both ends of (for example) a phage genome.Termination condon is one of three triplet sequences, UAG (amber), UAA (ochre), or UGA that cause

11、termination of protein synthesis; they are also called nonsense codons.terminator is a sequence of DNA. represented at the end of the transcript, that causes RNA polymerase to terminate transcription.Tertiary structure of a protein describes the organization in space of its polypeptide chain. Testcr

12、oss involves crossing an unknown genotype to a recessive homozygote so that the phenotypes of the progeny correspond directly to the chromosomes carried by the parent of unknown genotype.Thalassemia is diease of red blood cells resulting from lack of either or glogin.Thymine dimmer comprises a chemi

13、cally crosslinked pair of adjacent thymine residues in DNA, a result of damage induced by ultraviolet irradiation.Topoisomerase is an enzyme that can change the likning number of DNA (in steps of 1by type I; in steps of 2 by type II).Topological isomers are molecules of DNA that are identical except

14、 for a difference in linking number.Tracer is a radioactively labeled nucleic acid component included in a reassociation reaction in amounts too small to influence the progress of reaction.Trailer is a nontranslated sequence at the 3 end of an mRNA following the termination condon.Trans configuratio

15、n of two sites refers to their presence on two different molecules of DNA (chromosomes).Transcribed spacer is the part of an rRNA transcription unit that is transcribed but discarded during maturation; that is, it does not give rise to part of rRNA.Transcription is synthesis of RNA on a DNA template

16、.Transcription unit is the distance between sites of initiation and termination by RNA polymerase; may include more than one gene.Transduction refers to the transfer of a bacterial gene from one bacterium to another by a phage; a phage carrying host as well as its own genes is station and transfer o

17、f eukaryotic cellular sequences by retroviruses.Transfection of eukaryotic cells is the acquistion of new genetic markers by incorporation of added DNA.Transformation of bacteria describes the qcquisition of new genetic markers by incorporation of added DNA.Transformation of eukaryotic cells refers

18、to their conversion to a state of unrestrained growth in culture, resembling or identical with the tumorigenic condition.Transgenic animals are created by introducing new DNA sequences into the germ line via addition to the egg.Transit peptide is the short leader sequence cleaved from proteins that

19、are imported into cellular organelles by post-translational passage of the membrane.Transition is a mutation in which one pyrimidine is substituted by the other or in which one purine is substituted for the other.Translation is synthesis of protein on the mRNA template.Translocation of a chromosome

20、describes a rearrangement in which part of chromosome is detached by breakage and then becomes attached to some other chromosome.Translocaation of a gene refers to the appearance of a new copy at location in the genome elsewhere from the original copy.Translocation of a protein refers to its movemen

21、t across a membrane.Translocation of the rigbosome is its movement one codon along mRNA after the addition of each amino acid to the polypeptide chain.Transmembrane protein is a component of a membrance; a hydrophobic region of regions of the protein resides in the membrane, and hydrophilic regions

22、are exposed on one or both sides of the membrane.Transplantation antigen is protein coded by a major histocompatibility locus, presuent on all mammalian cells, involved in interactions between lymphocytes.Transposaes is the enzyme activity involved in insertion of transposon at a new site.Transposti

23、on immunity refers to the ability of certain transposons to prevent others of the same type from transposing to the same DNA molecule.Transposon is a DNA sequence able to insert itself at a new location in the genome (without any sequence relationship with the target locus).Transpostion refers to th

24、e movement of a transposon to a new site in the genome. See also nonreplicative transposition, replicative transposition, and conservative transposition.Transvection describes the ability of a locus to influence activeity of an allele on the other homoloue only when two chromosomes are synapsed.Tran

25、sversion is a mutation in which a purine is replaced by a pyrimidine or vice versa.True-breeding organisms are homozygous for the trait under consideration.Twisting number of a DNA is the number of base pairs divided by the number of base pairs per turn of the double helix.Underwinding of DNA is pro

26、duced by negative supercoiling (because the double helix is itself coiled in the opposite sense from the intertwining of the strands).Unequal crossing-over describes a recombination event in which the two recombining sites lie at nonidentical locations in the two parental DNA molecules.Unidirectiona

27、l replication refers to the movement of a single replication fork from a given origin.Uninducible mutants cannot be induced.Unscheduled DNA synthesis is any DNA synthesis occurring outside the S phase of the euikaryotic cell.Up promoter mutations increase the frequency of initiation of transcription

28、.Upstream identifies sequences proceeding in the opposite direction from expression; for example, the bacterial promoter is upstream from the transcription unit, the initiation codon is upstream of the coding region.URF is an open (unidentified) reading frame, presumed to code for protein, but for w

29、hich no product has been found.V gene is sequence coding for the major part of the variable (N-termainal) region of an immunoglobulin chain.Variable region of an immunoglobulin chain is conded by the V gene and varies extensively when different chains are compared, as the result of multiple (differe

30、nt) genomic copies and changes introduced during construction of an active immunoglobulin.Variegation of phenotype is produced by a change in genotype during somatic development.Vectorsee cloning vector.Vesicles are small bodies bounded by membrane, derived by budding from one membrane, often able t

31、o fuse with another membrane.Virion is the physical virus particle (irrespective of its ability to infect cells and reproduce).Virulent phage mutants are unable to establish lysogeny.Wobble hypotheis accounts for the ability of a tRNA to recognize more than one condon by unusual (non-GC,AT) pairing

32、with the third base of a codon.Writhing number is the number of times a duplx axis crosses over itself in space.Zero time-binding DNA enters the duplex form at the start of a reassociation reaction; results from intramolecular reassociation of inverted repeats.Zinc finger protein has a repeated motif of amino acids with characteristic spacing of cysteines that may be invoved in binding ainc; is characteristic of some proteins that bind DNA and /or RNA.Zoo blot describes the use of Southern blotting to test the