分子生物學(xué)4chapter9

1、chapter 9: chapter 9: the mutability and repair of dnamutationrecombinationhomologous recombination (同源重組）同源重組）site-specific recombination(位點(diǎn)專一重組位點(diǎn)專一重組) transposition ( 轉(zhuǎn)座）轉(zhuǎn)座）the causes of mutationvmutagensverror in replicationchemical physicalensuring the accuracy replication errors cause types poi

2、nt mutation insertions or deletionsntautomerism on base-pairingndna polymorase ithe nature of mutations point mutations: 1. transitions (pyrimidine to pyrimidine, purine to purine)2. transversions (pyrimidine to purine, purine to pyrimidine)insertions or deletionsatg,gtg,gag,ccg,gcc,gag,tagatg,gtg,g

3、ag,ctg,gcc,gag,tagatg,gtg,gag,ccg,gcc,gag,tagatg,gtg,gag,cg,gcc,gag,tagatg,gtg,gag,cgg,ccg,agt,agpoint mutationinsertions or deletionsmissenselerrors in replicationreplication errors and their repairlrepair of replication errors: mismatch repair increase the accuracy of dna synthesis for 2-3 orders

4、of magnitudes.prokaryote eukaryotemismatch repair removes errors that escape proofreadingtwo challenges:1 rapidly find the mismatches/mispairs2 accurately correct the mismatchprokaryote mismatch repairdna is kinkedmuts is a dimer. one monomer interacts with the mismatch specifically, and the other n

5、onspecifically.different exonucleases are used to remove ssdna between the nick created by muth and the mismatch.exonuclease vii or idna polymerase iiidam methylase methylate a residues on both strands of 5-gatc-3replication generate hemimethylation dna in e.colimuth makes incision unmethylated daug

6、hter strandlerrors in replicationreplication errors and their repairlrepair of replication errors: mismatch repair increase the accuracy of dna synthesis for 2-3 orders of magnitudes.prokaryote eukaryoteeukaryotic cells also repair mismatches and do so using homologs to muts (msh) and mutl (mlh). th

7、e underlying mechanisms are not the same and not well understood.dna damage and their repairdirect reversal of dna damagebase excision repair nucleotide excision repairrecombination (dsb) repairstranslesion dna synthesisdamage spontaneouslalkylation, oxidation and radiation base analogs intercalatin

8、g agentsdna undergoes damage spontaneously from hydrolysis and deaminationdeamination cuhydrolysis creates apurinic deoxyribose deamination 5-mc t explaining why dna contains t instead of ualkylation, oxidationnitrosamines (亞硝胺)reactive oxygen species (o2-, h2o2, oh)radiationbase analogspoint mutati

9、on intercalating agentsinsertion or deletiontwo consequence of dna damagesuch as thymine dimer, nick or breaks in the dna backbone,that has no effect on replication but cause mispairing, which in turn can be converted to mutation.dna damage and their repair direct reversal of dna damage base excisio

10、n repair nucleotide excision repair recombination (dsb) repairs translesion dna synthesisdamage spontaneouslalkylation, oxidation and radiation base analogs intercalating agentsdamage spontaneouslalkylation, oxidation and radiation base analogs intercalating agentsdirect reversal of dna damagephotor

11、eactivationmonomerization of thymine dimers by dna photolyases in the presence of visible light.methyltransferase catalyzes the transfer of the methyl group on o6-methylguanine to cystein residue on the enzyme, thereby restoring the normal g in dna.methyl group removalbase excision repairap endonule

12、ase & exonulcease cleaves the abasic sugarsdna polymerase/ligase works sequentially to complete the repair event.glycosylaserecognizes the damaged baseremoves the damaged baseoxog:a repair. a glycosylase recognizes the mispair and removes a. fail-safe systemsnucleotide excision repair1. recognize di

13、stortions to the shape of the dna double helix2. remove a short single-stranded segment that includes the lesion. 3. dna polymerase/ligase fill in the gap.transcription-couple repair: nucleotideexcision repair system is capable of rescuing rna polymerase that has been arrested by the presence of les

14、ions in the dna templaterecombination repairsdouble-strand break (dsb) repair pathwayfigure 10-4. damage in the dna template can lead to dsb formation during replicationfigure 10-3 dsb repair model for homologous recombination translesion dna synthesisoccurs when the above repairs are not efficient enough so that a replicating polymerase encounters a lesion1. translesion synthesis is catalyzed by a specialized class of dna polymerases that synthesi