DNA repair and Maintenance of Genome Stability

Question 1

What is a transition mutation?

Answer 1

Pyrimidine to Pyrimidine

T->C

Question 2

What is a transversion mutation?

Answer 2

Pyrimidine to purine

T->G

Question 3

Types of pyrimidine

Answer 3

Cytosine

Thymine

Question 4

Types of purines

Answer 4

Adenine

Guanine

Question 5

What can induce DNA damage

Answer 5

UV light

Question 6

Give an example of when can mutations be advantageous?

Answer 6

When the cells only survive in arginine, they can mutate so that you can live without arginine present

Question 7

What is a nucleotide?

Answer 7

A bass + sugar + phosphate backbone

Question 8

what can point mutations cause?

Answer 8

stop codons
silent mutations
point mutations - effects gene function

Question 9

How is DNA read?

Answer 9

triplet codons

Question 10

What are the consequences of mutations?

Answer 10

Gene amplification
Broken genes 
Fused genes 
Altered genes 
Missing code 
Damaged gene

Question 11

What causes mutations?

Answer 11

Luck 
Inherited predisposition 
Environmental:
External e.g. smoking 
Internal e.g. free the metabolised oxygen which attack the DNA

Question 12

Know the types of DNA damage

Answer 12

Nucleotide damage (UV light) e.g. pyrimidine dimer
Abasic site (hydrolysis)
Base damage:
- Cytosine deamination e.g. uracil
- Alkylating agents e.g. 06 methyl adenine
- Reactive oxygen e.g. oxoguanine

Question 13

cause does depurination cause?

Answer 13

spontaneous reaction with water

Question 14

what is the consequence of depurination?

Answer 14

base loss

Question 15

What causes mutations?

Answer 15

Replication, a base change does not cause the mutation, it is the replication with the base change

Question 16

What causes deamination?

Answer 16

Spontaneous, specialist deaminases

Question 17

What is the result of deamination?

Answer 17

Mismatch

Question 18

What is the reactive species equation?

Answer 18

Oxygen -> Superoxide -> Hydrogen peroxide -> Hydroxyl radical

Question 19

Name the reactive oxygen species which are dangerous

Answer 19

Superoxide
Hydrogen peroxide
Hydroxyl radical
Peroxisomes

Question 20

What produces reactive oxygen species?

Answer 20

Mitochondria

Question 21

What is the consequence of reactive oxygen species?

Answer 21

Base mispair

Question 22

Consequences of UV light?

Answer 22

Mispair

Question 23

What does UV form?

Answer 23

covalent bonds between adjacent bases between pyrimidine

Question 24

What is the result of reactions with alkalyting agents?

Answer 24

loss of base, misread during replication

Question 25

what is the conequences of bulky adducts?

Answer 25

non-coding base

Question 26

Why does bulkby adducts cause mutations?

Answer 26

body tries to excrete chemicals, cytochrome p450 tries to let you pee them out, makes it more reactive and it is the derivatives of the chemicals which attack your DNA

Question 27

What does alcohol cause?

Answer 27

chemicals which interact with both strands of the DNA meaning you cannot pull them apart `

Question 28

Why do mutations happen all of the time?

Answer 28

There is not enough genes in the body to encode for all of the functions of the immune system so these genes are segmented because it is confident that it is able to repair them

Question 29

Explain proofreading

Answer 29

DNA polymerase adds the wrong nucleotide, it recognises them and goes back to remove them and then able to extend it

Question 30

What is the DNA repair pathway for mis-matched bases?

Answer 30

Mismatch repair

Question 31

What is the DNA repair pathway for base damage?

Answer 31

Base excision repair

Question 32

What is the DNA repair pathway for nucleotide damage?

Answer 32

Nucleotide excision repair

Question 33

What is the DNA repair pathway for DNA breaks?

Answer 33

Non-homologous end joining Microhomology mediated joining Homologous recombination

Question 34

Describe mismatch repair in eukaryotes

Answer 34

There is a nick in the newly synthesised strand Protein (MSH) binds to the nick and causes it to form a loop The newly synthesised strand is digested Insertion of nucleotides to fix the strand

Question 35

Describe mismatch repair in prokaryotes

Answer 35

There is a nick in the newly synthesised strand The old strand is methylated so the protein knows which one the old one is Protein (MutS) binds to the nick and causes it to form a loop The newly synthesised strand is digested Insertion of nucleotides to fix the strand

Question 36

Describe base excision repair

Answer 36

The base is removed by glycosylase Sugar phosphate is removed by AP endonuclease and drp lyase Gap is filled by polymerase and DNA ligase

Question 37

Describe nucleotide excision repair

Answer 37

Pyrimidine dimer - DNA damage recognise Helicase unwinds the DNA around damage and nucleases cut section of damaged strand 5' and 3' to damage DNA polymerase and ligase

Question 38

Describe non-homologous end joining

Answer 38

'clean break', ends held together by Ku70/80 | DNA ligase joins ends

Question 39

why is non-homologous end joining error prone?

Answer 39

there can be a dirty break and this results in loss of base pairs - deletion mutation

Question 40

Describe microhomology end joining

Answer 40

``` 'dirty', non-ligatable ends DNA ends resect to produce single strand DNA Complimentary DNA strands revealed Pairing of complimentary ends Ligated by DNA ligase ```

Question 41

Describe homologous recombination

Answer 41

``` Sister chromatids CtIP DNA ends resected to generate single strand DNA RAD51 Homology search and strand invasion DNA synthesis and branch migration 'Missing' information replaced DNA ligation ```

Question 42

Example of a DNA repair signature

Answer 42

scars