Mutation

Question 1

What is a transition mutation?

Answer 1

. SNP mutation (substitution)

. Purine swapped for purine, or pyrimidine swapped for pyrimidine

Question 2

What is a transversion mutation?

Answer 2

. SNP mutation (substitution)

. Purine swapped for pyrimidine, or pyrimidine swapped for purine

Question 3

Which agent increases the risk of transitions?

Answer 3

Nitrous acid

Question 4

Which agent increases the risk of transversions and methylation?

Answer 4

Alkylating agents

Question 5

What is the difference between purines and pyrimidines?

Answer 5

Purines have two rings, pyrimidines have one

Question 6

What does the Ames test indicate?

Answer 6

. Presence of mutagenesis

. Uses bacteria that can’t make histidine –> reversion to histidine indicates mutagenesis

Question 7

How are pyrimidine dimers restored? Which enzyme catalyses this?

Answer 7

Photoreactivation, catalysed by DNA photolyases

Question 8

What does alkyltransferase do?

Answer 8

Reverses methylation of bases (usually caused by alkylating agents)

Question 9

Which protein is involved in mismatch repair?

Answer 9

Mut protein

Question 10

Which DNA repair methods are used when a lesion affects only one DNA strand?

Answer 10

Base excision repair or nucleotide excision repair (correct pyrimidine dimers)

Question 11

What is non-homologous end joining (NHEJ)? Which protein detects DNA break?

Answer 11

. Repair for double strand break
. Ku protein detects broken DNA
. Ends of DNA aligned and ligated

Question 12

What is homologous/recombinant end joining (HEJ)?

Answer 12

. Double stranded breaks joined at Holliday junctions to give single stranded ends
. Ligated

Question 13

Which two genes are involved in homologous recombination?

Answer 13

BRCA1 and BRCA2

Question 14

Which DNA repair methods are used in double stranded breaks?

Answer 14

NHEJ and HEJ