Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
42 Cards in this Set
- Front
- Back
|
what 2 types of mutations exist |
1. spontaneous 2. induced |
|
|
explain the spontaneous mutation - deamination |
removal of an amine group from cytosine ---produces uracil C--->U |
|
|
what does deamination of 5'methyl cytosine produce |
thymine |
|
|
what is depurination |
removal of a purine from DNA |
|
|
what harm do reactive oxygen species bring |
-products of oxygen metabolism -superoxide,hydrogen peroxide and hydroxy radicals -guanine particularly susceptible |
|
|
what are tautomeric shifts |
-temperory changes in base structure. -tautomers(bases) exist is 4 forms - enol,keto,amino and imino |
|
|
what is the stable form of T and G bases |
keto keto can convert to enol |
|
|
what is the stable form of A and C bases |
amino amino can convert to imino |
|
|
what are trinucleotide repeats |
trinucleotide repeat expansion - a repeated sequence can increase in number from one generation to the next (usually a CAG repeat) e.g. huntingtons disease and fragile X syndrome |
|
|
what are induced mutations |
induced by mutagens |
|
|
what are the 2 types of mutagens |
1. chemical 2. physical |
|
|
what processes come under chemical mutagens |
1. base analogues 2.base modifiers 3.interclating agents |
|
|
what do base modifiers do |
covalent modification of base structure |
|
|
what does alkylation do |
tranfer of methyl,ethyl and other larger alkyl groups to DNA -distorts the structure of double helix |
|
|
where does the alkylation take place |
-on the nitrogen and oxygen atoms external to the base ring systems -nitrogen atoms in the base system except those attached to the deoxyribose on the DNA -non-bridging oxygen atoms in phosphate groups |
|
|
what are the 2 types of repair system for single base changes |
1. direct reversal 2. excision repair |
|
|
what is the process in direct reversal in DNA repair |
dealkylation |
|
|
describe the process of dealkylation and the enzyme used |
enzyme - MGMT - O6-Me-Guanine-DNA -methytransferase protects by transferring methy groups on to its own cytosine residues protects against DNA O6-me-guanine DNA lesions |
|
|
what does AlkB do |
removes methyl groups from all bases repairs 1-Me A and 3-Me C by oxidative demethylation |
|
|
describe base excision repair |
-damaged base is removed -triggering short or long patch repair -short patch repaired by pol-beta -long patch repaired by pol-epsilon/delta -one of 2 pathways triggered depending on how base is removed. |
|
|
what do DNA glycosylases do |
remove a base by cleaving the bond between deoxyribose sugar and the base (using H2O) |
|
|
what do lyases do |
they open the ring structure of deoxyribose sugar (using NH2) |
|
|
removal of the damaged base by glycosylase leads to 2 pathways. what are those? |
a GAP or nick is produced by removing the deoxyribose phosphate from the DNA backbone by: 1. 5' AP endonucelase phosphodiesterase (APE) 2. or a lyase |
|
|
what are the structural distortions to DNA |
1. photodimerism 2. Adduct formation 3. Intercalation |
|
|
explain adduct formation |
benzo(a)pyrene is carcinogenic constituent of cigerette smoke other compounds forming bulky adducts on DNA cisplatin - cancer chemotherpeutic compound |
|
|
explain photodimerism |
UVA-320-400-harmless UVB-295-320-Damage to skin UVC-100-295-little comes to earth because of ozone layer -dimers between adjacent pyrimidines are formed CPD - cyclobutane pyrimidine dimer accounts for most UV induced damage -produces a kink in DNA |
|
|
what causes intercalation |
acridines, ethidium bromide and proflavins |
|
|
describe intercalation |
flat planar structure or ring structure molecules that interacts with DNA in the double helix and insert themselves into the duplex - stretching it -DNA pol inserts an extra base opposite an intercalated molecule -can result in nucleotide addition or deletion - frameshift occurs |
|
|
what is mismatch repair (MMR) |
a repair system that repairs distortions introduced by mispaired bases shortly after replication. -repairs ONLY daughter strands |
|
|
how does the cell know which is parental strand and which is daughter strand |
the parental strand contains different epigenetic tags compared to daughter strands |
|
|
how does mismatch repair take place |
at replication form, only parental strand carries methyl tags. these methyl tags recogonised by Mut H, which interacts with Mut S - which detects the damage |
|
|
what are the repair system involved in mismatch repair of prokaryotes |
Mut S, Mut H and Mut L |
|
|
what happens in nucleotide excision repair |
an excision repair pathway that recognises bulky lesions in DNA. used to repair adducts and photodimers |
|
|
what are the 2 subpathways of nucelotide excision repair |
1. global genome repair 2. transcription couples repair |
|
|
what is the eukaryotic nucleotide excision repair pathway |
1. damage recognition 2. incision in the damaged DNA strand on each side of the lesion. 3. excision of the oligonucleotide created by the incisions 4. synthesis of new DNA to replace excised DNA 5. ligation of the nick |
|
|
what is the damage recognition done by in global genome repair |
XPC and HHR238 |
|
|
what is the full form of XPC |
xeroderma pigmentosum C gene |
|
|
how does DNA unwinding take place in global genome repair |
done by the helicase avtivity of the transcription factor TH11H, a large complex which contains 2 other products of the XP genes XPB and XPD - both helicases |
|
|
what is the next step after DNA unwinding in global genome repair |
dual incision on either side of the lesion on one strand |
|
|
how does the dual incision take place |
binding of RPA - singe stranded binding protein endonucleases encoded by XPG and XPF protein XPG - cuts on 3'end XPF - cuts on 5'end with ERCC1 20-30 nucleotides excised |
|
|
how does repair by a synthesis of new strand take place |
synthesis by pol epsilon/delta nick translation sealed by DNA ligase (Ligase 3 and XRCC1 complex) |
|
|
what is the difference between global genome repair mechanism and nucleotide coupled repair mechanism |
the damage recognition XPC in global genome RNA polymerase 11 in nucleoide coupled repair |
