DNA damage Flashcards
Cancer results mainly from?
Mutation that arise mainly in DNA damage
DNA damage?
modification in the molecular structure of genetic material
Two ways which DNA damage can arise?
endogenously: normal metabolism in the cell such as DNA replication and repair
exogenously: environmental sources
DNA damage types
- Spontaneous DNA damage
2. Environmental DNA damage
DNA repair exists in which organisms?
Both pros and eus
Proteins In DNA repair?
Highly conserved throughout evolution
Genetic disorder types due to DNA damage
- Ataxia-telangiectasia (AT)
- Degenerative motor condition caused by the failure to repair oxidative damage in the cerebellum
- Xeroderma pigmenosum (XP)
XP?
a condition characterized by sensitivity to sunlight and linked to a defect in an important ultraviolet UV damage repair pathway
DNA damage repair gene example
RAD group
DNA repair processes can be categorised by the functional nature of the repair mechanisms into which three groups
Reversal of base damage
excision of base damage
repair of double strand breaks
Function of MTS-alpha
recognition of small loops generated by insertions or deletions of NT as well as single base mismatches
MUTS-alpha structure?
Hetro-dimer of MSH2 and MSH6
MUTS-beta structure and function?
Made up of MSH2 and 3
recognition of small loops during MMR
Subsequent to mismatch recognition, which hetrodimeric complexes are involved?
PROTEINS
MLH1 PMS2 AND MLH3
Common cancers caused by MMR?
colon, utrine, ovarian, gastric
NT excision repair technique, associated with what type of cancer
excision of approximately 30 NT around the damaged site Is used to repair a wide variety of bulky lesions and associated with skin cancer
3 formal stages of NER include?
- damage recognition
- dual incision
- Repair synthesis and ligation
What is XPC, function, in what type DNA repair process is it involved in?
XPC- A protein called C originally idenitided in patients with zeroderma
stably binds to another protein called HHRAD23
HH- human homologue
reversal of base damage?
Enzyme characteristics
Direct repair
DNA damage repaired by which the normal structure is restored.
Single enzyme composed of a single polypeptide chain catalyses a single step reaction
Reversal of base damage involves the/..?
breakage and repair of abnormal bonds
Example of reversal of base damage and the enzyme required
Photoreactivation (PR) of DNA:
- Repair of pyrimidine dimers
- enzyme DNA photolyase (photoreactivating enzyme, deoxyribodipyrimidine photolyases).
Gene encoding DNA photolase in placental mammals
gene lost
Other enzyme which are involved in direct repair include?
6-4 photoproduct lyase, Spore photoproduct lyase, O6-methylguanine DNA methyltransferase
Excision of base damage includes?
mismatch repair, NT excision repair, Base excision repair
excision of base damage mechanisms involve? mediated by
a physical removal and replacement of damaged bases mediated by a range of Dif enzyme complexes
The enzymatic process is dedicated primarily to the ?
Excision fo NT that are incorrectly paired with the (correct) NT on the opposite strand
the formation of XPC -HHRAD23 is then followed by?
The hetrodimeric complex is then followed by the the recruitment of of other proteins to the site
XPA, RPA, TFIIH AND XPG
Which proteins recruited in addition to the XCP-HHRAD23 hetrodimeric complex are involved in the recognition of damaged DNA
XPA and RPA
Structure and function of TFIIH
two subunits with helicase activities;
viz, XPB, XPD that unwind the DNA locally creating a bubble in the DNA
Function of ERCC1 and XPF binding the hetrodimeric complex: XPC-HHRAD23
generate a complete assembly fo the NE repairosome
Describe the process of bimodal incision of DNA and excision of a fragment?- NER
- XPG, a DNA nuclease recruited by RPA/TF11H makes a 3’ incision 3-5 NT from the damaged site
- The ERCC1-XFP makes a 5’ insision24-25 from the damaged site on the same strand
- This bimodal incision generates a 27-30 NT fragment which include the damaged base
Repair synthesis and ligation process in NER
RFC molecular matchmaker loads PCNA trimeric circle onto DNA by dissociating the post incision complex
association with DN pol e and d, resaving with repair synthesis proteins
the gap is filled and repair is ligated
Fill in the blanks
BER replaces missing or modified ……….. ………. with its the correct …… …., which is not recognised by the …… ……………. and involves ………….. and ………….. of one ……….. …………
DNA bases DNA base NER machinery excision and replacement single base
Most common damage repaired by base excision repair?
cytosine deamination to uracil by UV (typically)
Base excision repair is initiated by? Process of initiation
DNA-repair-specific enzymes- DNA glycosylases
recognises a single or small subset of chemically altered or inappropriate bases
Fill In the blanks
an enzyme called ……… ……-……… specifically recognises ……… as an inappropriate base in DNA and catalysis …….. of the …-………….. bond which links the base to the ……..-………… …………….
uracil DNA-glycosylase uracil hydrolysis N-glycosidic bond sugar-phosphate bond
why is excision repair initiated by DNA glycolases called base excision repair
bases removed as free bases
removal of free bases in base excision repair results in?
apurinic or apyrimidinic (AP) sites
AP or apurinic site are recognised by and its function
enzyme: Ape (apurinic/apyrimidinic) endonucelase
cuts DNA phosphodiester backbone at the 5’ site producing nicks in at this site by hydrolysis
deoxyribophosphodiesterases (drpakse)
exonuclease that degrade single strand DN and are to inhibited by an imcompletee NT. They are responsible for removing an entire NT
The sequential action of DNA glycol’s a 5’ AP endonuclease and the dRpase can generate …
a single nucleotide gap in the DNA duplex during base excision repair
function of PARP-1
poly(ADP-ribose) polymerase-1
assists the repair process by binding to single strand break intermediate and enhances the recruitment of pol b and CRCC1-DNA ligase
BER is resolved in a …… ………. or …….. ……….
long or short patch
In short patch repair?
the deoxyribose phosphate is removed and a single NT is inserted at the site of the break
In long patch repair?
up to 13 NT are inserted and the displaced strand entailing the abasic deoxyribose phos is cleaved by a “flap’ endonulease
repair is completed by a
ligase
repair of double stand breaks by either
homologous recombination (HR) or by non-homologous end joining (NHEJ)
When does homologous recombination normally occur? involves
during meiosis and involves the swapping of large homologs reigns of DNA by recombination
damaged sites are repaired by using ?- HR
using info on the undamaged homologous region on the chromosome
process of HR requires?
extensive sequence homology and multiple proteins
deficiencies in this repair mech leads to?
breast cancer (BRCA1 genes)
Non-homologous end joining (NHEJ) involves but does not require?
required: mutliprotein complex
not required: homologs regions on the chromosomes
one way in which base damage/ strand breaks are allowed to persist in a cell?
process of translation DNA synthesis
describe the process of translation DNA synthesis (
- replication machinery bypasses sites of base damage
- allowing DNA replication to proceed down stream of the unrelated damage site,
- but the use of a ‘sloppy’ polymerases which add NT to the replicating strand opposing the DNA lesion. –> mutations
