DNA repair

Question 1

ways that DNA molecules effected by chemical change

Answer 1

Thermal degradation (heat/water)

Metabolic byproducts (oxidation)

Environmental substances (benzopyrene)

Radiation (UV, nuclear fission)

Question 2

Difference between purine and pyrimidine

Answer 2

G and C (3 h bonds)
T and A and U (2 bonds)
G and A double ring purines
T and C single ring pyrimidine

Question 3

difference between transition and transvehrsion mutations

Answer 3

transition - double ring for double ring or single for single

transversion - single for double vice versa

transition more likely and doesn’t often cause change in AA

Question 4

Uv light causes…

Answer 4

formation of pyrimidine dimers

Question 5

what is a pyrimidine dimer

Answer 5

two T or C connect together forming protrude of backbone, cannot replicate easily

Question 6

what can cause Double stranded DNA breaks

Answer 6

ionising radiation, free radicals/ oxidation, replication errors

Question 7

what is deamination

Answer 7

hydrolysis of C. to U releasing ammonia

Question 8

what is depurination

Answer 8

glycosidic bond hydrolysed releasing A OR G

Question 9

how do free radicals cause DNA damage

Answer 9

attack both bases and backbone
carcinogenic
they steal electrons from DNA by oxidation

Question 10

when is base excision repair required

Answer 10

following oxidation, deamination and alylation

Question 11

steps in base excision repair

Answer 11

1. cleave the inccorrect tase by DNA glycosylase
2. AP endonuclease and phosphodiesterase remove the backbone (sugar phosphate)
3. DNA polymerase adds new nucleotide
4. ligase seals nick

Question 12

How do the glycosylases identify errors in DNA

Answer 12

use the base flipping strategy

Question 13

What is nucleotide excision repair used for

Answer 13

to remove pyrimidine dimers

Question 14

steps in nucleotide excision repair

Answer 14

1. Excision nuclease removes section of ssDNA
2. DNA helicase unwinds DNA and pulls away from strand
3. polymerase and ligase fill in the gaps with correct sequence

Question 15

what and how is translational DNA polymerase used. what a re the disadvantages

Answer 15

recruited by the sliding clamp to remove covalent modifications and to synthesise
it is not as precise and doesn’t proof read as well so can get single base changes mutations

Question 16

2 mechanisms used to repair dsDNA damage

Answer 16

non homologous End joining

and

homologous recombination

Question 17

steps in non homologous End joining

Answer 17

1. end recognition by Ku Heterodimers
2. additional portions, DNA-PK and ATM protein kinases attach
3. repair synthesis and ligation

Question 18

steps in homologous recombination

Answer 18

1. using sister chromatid
2. digestive 5’ end using nuclease
3. unwind sister and use as template
4. go back to original complimentary strand
5. DNA ligation

Question 19

what occurs if issue with. homologous recombination

Answer 19

cause cancers and diseases