L4 - genome stability

Question 1

difference between mutation and DNA damage

Answer 1

damage to DNA can be temporary
- time for it to be fixed before replication

after 2 rounds of semi-conservative replication = mutation = apart of genome

Question 2

2 most common causes of DNA damage (in order)

Answer 2

1. Deurination
   water attacks N-glycosyl bond between sugar and base = abasic site
2. deamination
   water attacks cytosine removing amine group-NH2
   = produces Uracil base

= easier to resolveas we have proteins that recognise uracil as not meant to be in DNA

Question 3

what happens when metal-cytosine is attacked by water instead of just cytosine and why is this damage harder to detect

Answer 3

when 5-methyl cytosine loses amine group -NH2

produces thymine base
= harder to detect

Question 4

what is alkylation in terms of DNA damage

Answer 4

alkylation is the addtion of a methyl group

can be added to worng base

methyl-guanine forms base pairs with thymine

Question 5

what is 8-oxo-guanine

Answer 5

form of DNA damage caused by reactive oxygen species (ROS)

can base pair with cytosine AND adenine

= risk is minimised for nuclear DNA as no Oxygen present
= mitochondrial DNA more at risk

Question 6

what kindve DNA damage is smoking linked to

Answer 6

Benzopyrenes

adds benzopyrene to guanine blocking replication and transcription

Question 7

what does UV light cause in terms of DNA damage

Answer 7

pyrmidine dimers

adjacenet T + C bases froma dimer blocking transcription and replication

Question 8

what is photoreactivation - repair

Answer 8

reverses UV damage/pyrmidine dimer by direclty reversing chemistry

DNA photlyases are flavoproteins - redox-active cofactor breaks the cyclobutane ring

= widely distributed in prokaryotes but not humans

Question 9

DNA-alkyltransferases - direct reversal 2

Answer 9

protein snips and accepts methl group

= not a enzyme as protein degrades afrter reaction
= not reversible