生化c15dnadamageandrepair

1、biochemistrydept. of biochemistry and molecular biologyprofessor wu yaosheng2014-05dna damage and repair case onewhywhy？xeroderma pigmentosum, xpsection 1 dna damage section 2 dna repairsection 3 significance of dna damage and repair4main contentsdna damage；the factors to induce dna damagetypes of d

2、na damage：structural failure；mismatch；breakage；covalent linkage；manner of dna repair：direct repair；excision repair；recombinant repair； translesion repair 5key points1. what is the relationship between dna correct replication and dna mutation?4. whether local space ultraviolet disinfection used commo

3、nly in clinical also can be used for disinfection on the surface of human body? why is that?3. pickled fish hot pot is delicious, but whether is it fit to be often eaten? why is that?2.why could dna generate damage? 65.which one of dna damage repair mechanisms in human body is the most effective? wh

4、y? the changes of dna composition and structure caused by various factors in vivo or in vitro is called as dna damage 1.dna mutation, permanent alteration of dna structure 2. the function of dna as replication or transcription template is lostthe results induced by dna damage :7biological diversity

5、dependent on：dna mutationdna repair balance 8dna damage1. dna damage are caused by different mechanisms 1.1 factors in vivo dna replication error dna itself instability reactive oxygen generated by metabolism in vivo10dna replication errorsinterconversion of base pair during dna replication, imbalan

6、ce of dntp concentration rate of mismatch of dna replication is about 1/1010missing or insertion of dna fragmentalteration of copy number of repeat sequence, especially short tandem repeat sequence11fig 1 spinocerebellar ataxia type3 gxpl01 pedigree (cga repeat)12spinocerebellar ataxia type 3 (sca3)

7、 , machadojoseph disease (mjd) 13spinocerebellar ataxia type 3 (sca3) , machadojoseph disease (mjd) ndna itself instability:dna itself structure instability is the most frequent and important factor to cause dna spontaneous damagewhen dna is heated or environment ph changes, dna molecular glycosidic

8、 bond between base and ribose can hydrolyze spontaneously, leading to the loss of base or fall off, of which the most occur depurination.spontaneously deamination, from one base to another base, for example, c to u, a to i, so on.141.2 factors in vitrophysical factors chemical factorsbiological fact

9、ors nphysical factors：ionization radiation, ultraviolet( uv)16nchemical factors：dna damage induced by free radical dna damage caused by base analogue dna damage generated by base repair reagent, alkylate reagent dna damage induced by embed dye17dna damage caused by physical & chemical factors 182. t

10、he types of dna damagefall off of base (depurination)damage of base structureformation of pyrimidine dimer breakage of single strand dna or double strand dnadna covalent linkage 19nbase damage and glycosyl damagebase natures would be altered through group (radical) modification by some chemical toxi

11、cant instable bases on dna strands would be generated due to the damage of base or glycosyl, resulting in the breakage of dna strands20nmismatch between base pair：induced by insertion of base analogue, or action by base repair reagentspontaneous base mismatch during dna replicationthymine is replace

12、d by uracil inserting in dna21nbreakage of dna strands：caused by ionizing radiation, chemical toxicant, breakage of phosphodiester bond, deoxyribose damage, fall off or damage of base local denaturation of dna by base damage or glycosyl group and formation of sensitive site to nuclease, resulting in

13、 the breakage of dna strands the formation of apurinic-apyrimidinic site, ap site, or abasic site by dna glycosylase, breakage of dna at the ap site would more easily occur22ndna covalent linkagepdna intrastrand cross-linkingpdna interstrand cross-linkingpdna-protein cross-linking23dna damage could

14、cause the cases belowreplace of basedeletion of base insertion of base breakage of strandtransition transversion 24the repair of dna damage dna repair means that mismatch base pair could be corrected, impaired base or glycosyl group are eliminated dna repair is the key to maintain the integrity and

15、stability of the dna structure, guaranteeing the life extension and stability of species 26the common dna damage repair ways repair ways photoactive repair base excision repair nucleotide excisionmismatch repair recombinant repair repair objects pyrimidine dimer damaged base pyrimidine dimer, altera

16、tion of dna double helix structure mismatch bases during replication or recombinant breakage of dna double strands enzyme or proteins related to dna repairphotolyase dna glycosylase, ap endonucleasee.coli: uvra,uvrb,uvrc & uvrdhuman: xpa、xpb、xpcxpg, et al.e.coli: muth,mutl,muts，human: mlh1,msh2,msh3

17、,msh6 et al.reca、ku、dna-pkcs、xrcc41. direct repair of dna direct repair of pyrimidine dimer direct repair of alkylated base direct repair of depurination site direct repair of single strand breakage28ndirect repair of pyrimidine dimer29ndirect repair of alkylated base30ndirect repair of depurination

18、 siteprebuild of glycosyl bond catalyzed by dna purine insertion enzyme,leading to the purine direct insertion, which has very high specificityndirect repair of single strand breakageprebuild of phosphodiester bond by dna ligase312. excision repair of dna damagebase excision repairnucleotide excisio

19、n repair32nbase excision repair to recognize and to hydrolyze：the impaired base is recognized and hydrolyzed by dna glycosylase specifically, leading to the abasic site to cut off：the phosphodiester bond at 5-end of the depurination site is cut off, releasing the ribose phosphate to synthesize：the c

20、omplementary sequence is repaired on the gap by dna polymerase using the opposite strand as template linkage：by dna ligase, dna structure return normal3334nnucleotide excision repair first, the impaired dna fragment is recognized by one enzyme system; second, the impaired dna fragment is cut off fro

21、m its two sides; third, the complementary sequence is synthesized by dna polymerase, using another strand as template; finally, the gap is linked by dna ligase, the impaired dna is repaired completely.35ner in e.coli is consist of 4 kinds of proteinuvrauvrbuvrcuvrd 36nnucleotide excision repair of h

22、uman dna damage the impaired fragment is recognized by xpc,xpa, ssb binding to the impaired site of dna; xpb,xpd play the role of helicase, leading to form a bulge around the impaired dna; comformation of xpg & xpf is changed,exerting the endonuclase activity to cut the impaired fragment at 3-end an

23、d 5-end and release it, with the help of pcna; the remaining deletion region is repaired by polymerase or ; finally,it is linked by dna ligase 37not only ner repair the entire genome of damage dna, but also rescue the rna polymerase which has stopped work due to transcript template damage, called tr

24、anscription-coupled repairmode of action: ner was raised in the suspended rna polymerase the significance of transcription-coupled repair: the repair enzymes are focus on the transcription dna, the impaired dna would be repaired as soon as possible. 38nmismatch repairmismatch means the non watson-cr

25、ick base pair。it is one special form of base excision repair，and it is resposible to correct the followings: the mismatch base pair during replication and recombination; the mismatch base pair induced by base damage; the base insertion; the base deletion 39e.coli mismatch repair system to repair rep

26、lication mismatch3. recombination repair is needed for serious dna damage homologous recombination repairnon-homologous terminus linkage recombination repair41homologous recombination repair424.translesion dna damage repairtranslesion recombination repairtranslesion repair systhesis43sos repair, mechanism of lexa-reca operon 44the significance