4 基因突變與修復(fù).ppt

1、4.1. Point mutation 的類型, 突變的表達(dá)類型,-獲得突變型是遺傳學(xué)研究的重要前提,4.2. 突 變 發(fā) 生 的 機(jī) 理 (自發(fā)突變，誘發(fā)突變),4.2.1. 自發(fā)突變,4.2.1.1. 堿基異構(gòu)式引起DNA復(fù)制過(guò)程的錯(cuò)誤,a) 堿基異構(gòu)式,b) 堿基異構(gòu)式引起DNA復(fù)制的錯(cuò)配,堿基異構(gòu)式引起DNA復(fù)制的錯(cuò)配,C(i),C(a, anti),堿基異構(gòu)式引起DNA的錯(cuò)配突變,C(i),C(a),G(k, syn),G(k, syn),G(k, anti),G(k),4.2.2. 誘發(fā)突變,4.2.2.1. 物理誘變,a) 電離輻射誘變；,Co60 ()( ) ray Cs137

2、() () ray H3 () ray P32, S35() ray,()( ) ray穿透性 （外照射處理） () () ray非穿透性 （內(nèi)標(biāo)記處理）,dNt電荷及結(jié)構(gòu)改變,b) 非電離輻射Ultra Violet light (U.V),4.2.2.2. 生物技術(shù)定點(diǎn)誘變,4.2.2.3. 化學(xué)誘變,a) 干擾堿基合成的化學(xué)誘變劑,HNO2 (Nitrous acid NA),Base modifying chemical mutagen,Base modifying chemical mutagen,NH2OH (Hydroxylamine HA 羥胺),d) Alkylation a

3、gent mutagens,敏感位點(diǎn),Apurination (de-pu),e) Mutageninsertion-framshift,-ATTTTTCG - -TAAAAAGC-,-AT EB TTTTCG- -TA,分子插入,異相退火,-AAAAA-,-TTTTT-,X,AAAAGC-,T,A,4.3. 保證遺傳穩(wěn)定的機(jī)制,4.3.1. 復(fù)制過(guò)程中的錯(cuò)配修復(fù)機(jī)制 (= 10-11),DNApol (= 10-8) 經(jīng)第二次校正= 10-11,MRS Mismatch Repair System,4.3.1. Mismatch repair system,MCE scanning,endo

4、nuclease,Polymerase ligase,A,4.3.2 photo reactivation,-TT- -AA-,4.2.3 Excision repair Base excision repair (BER) - fixes abnormal bases (uracil, hypoxanthine, alkylated bases) Nucleotide excision repair (NER) - fixes large structural changes and helix distortions (pyrimidine dimers, bulky base adduc

5、ts),4 Steps: Recognize, Remove, Resynthesize, Religate,ung system (尿嘧啶-N-糖苷酶系統(tǒng)),-TAGC- -ATCG-,-TAGC- -A CG-,U,G,C,U,A,-TAGC- -A CG-,-TAGC- -A,TCG-,Base excision repair (BER),Base Excision Repair (BER),Nucleotide Excision Repair,NER machinery recognizes damaged regions in DNA based on their abnormal

6、structure as well as on their abnormal chemistry, then excises and replaces them.,In all organisms, NER has the same steps: Damage recognition Binding of a protein complex at the damaged site Double incision of the damaged strand several nucleotides away from the damaged site, on both the 5 and 3 si

7、des Removal of the damage-containing fragment from between the two nicks Filling in of the resulting gap by a DNA polymerase Ligation,2 UvrA proteins form a complex with one UvrB protein in an ATP-dependent reaction The complex recognizes UV damage by the bend in the helix The UvrA proteins dissocia

8、te from the complex after ATP hydrolysis. This leaves UvrB bound across from the damage,Nucleotide Excision Repair in E. coli,Now UvrB can recruit UvrC protein to the complex UvrC activates UvrB to nick the DNA 4 nts 3 from the pyrimidine dimer Then UvrB activates UvrC to nick the DNA 7 ntds 5 from

9、the pyrimidine dimer This leaves a fragment of DNA containing the damage that can now be removed,Nucleotide Excision Repair in E. coli,A helicase, UvrD, uses ATP hydrolysis to power the unwinding of the damaged DNA fragment. This reomoves UvrC The gap in the DNA is now filled in by DNAPI or II, reom

10、ving uvrB in the process Finally, DNA ligase seals the nick,Nucleotide Excision Repair in E. coli,Critical for repairing UV-induced damage (because we dont do direct repair) Principal is the same as in bacteria: But the proteins are different (20-30) Defects in NER proteins cause genetic disorders,N

11、ER in Humans,NER in HumansXeroderma pigmentosum (XP),Genetic disorder with symptoms: -extreme sensitivity to sunlight (by age 2), and 1000X higher risk of skin cancer (by age 8) Defect is in repair of UV damage Gene mapping identified 7 repair proteins (called XP proteins) XP-C and XP-A recognize py

12、rimidine dimers XP-B and XP-D have helicase activity XP-G and XP-F have nuclease activity,NER in Humans,XP-C recognizes pyrimidine dimers,XP-B and XP-D are helicases that separate the DNA strands around the damage,XP-G and XP-f are endonucleases that cut the DNA on either side of the damage,XP-A bin

13、ds to the pyrimidine dimer and helps to recruit other proteins to a complex,The cut fragment is removed and the gap is filled in by DNAP d or e,Rec-A. gene 以某種方式參與DNA損傷修復(fù),4.3.4. RecombinativeRepair,Rupp.Howard-Flanders,E.coli k12,A DNA molecule has a T dimer,this molecule is being replicated. A PolI

14、II will be unable to correctly copy the T dimer,DNA Pol II reinitiates DNA synthesis downstream of T dimers.,This cannot be repaired by the usual repair systems. However, the exposed ssDNA with the correctly synthesized daughter molecule,One daughter molecule still contains the T dimer but the oppos

15、ite strand has the correct sequence. The other daughter now contains a gap but this gap can be repaired correctly by the usual repair systems,4.3.5. SOS repair (U.V. reactivation or W reactivation),Jean Weagle, 80 10 100 mut. 100% 50% 10%,Damaged DNA of phage be repaired in E.coli A SOS repair in E. coli have to be induced by U.V. (A 三種功能,當(dāng)DNA復(fù)制受阻/ DNA damaged,能量大量消耗,當(dāng)DNA復(fù)制度過(guò)難關(guān)后,突變的形成,DNA,未經(jīng)修復(fù),經(jīng)過(guò)修復(fù) / 校正,突變是在修復(fù)過(guò)程中形成的（非準(zhǔn)確的修復(fù)）,4.4. 基因的回復(fù)突變 （back mutation / reverse mutation）,回復(fù)突變的概念,wild type,mutant (in phenotype),回復(fù)突變的分子機(jī)制,a) AGC (Ser) ACC (Thr) A