Causes of DNA Mutation - Lecture 17

Question 1

What is a mutation?

Answer 1

An alteration in the nucleotide sequence of a DNA molecule

Question 2

What are spontaneous mutations?

Answer 2

○ Mutations as a result of errors in DNA replication
○ Not common as DNA polymerases have proofreading activities

Question 3

What is strand-slippage?

Answer 3

Scenario 1:
○ Newly synthesised strand loops out
○ New strand has an extra nucleotide
Scenario 2:
○ Template strand loops out
○ Missing a nucleotide
○ Shifts reading frame so STOP codon appears earlier

Question 4

What are tautomers?

Answer 4

○ Isomers with slightly different chemical structures
○ Have different base-pairing properties

Question 5

What do the tautomers base pair to?

Answer 5

○ Tautomer of A pairs with C
○ Tautomer of T pairs with G
○ Tautomer of G pairs with T
○ Tautomer of C pairs with G (no change)

Question 6

What are mutagens?

Answer 6

Chemical or environmental agents that cause changes in DNA molecules

Question 7

How can mutagens cause mutations?

Answer 7

○ Base analogs: chemical incorporated into DNA
○ Direct structural change e.g. UV radiation

Question 8

What is 5-bromouracil?

Answer 8

○ An base analog of thymine
○ Used in cancer chemotherapy
○ Keto-5bU base pairs with A which is fine
○ Enol-5bU (more common) base pairs with G

Question 9

What are deaminating agents?

Answer 9

Change the structures of some nucleotides e.g. nitrous acid and sodium bisulphite

Question 10

What does deamination of the bases lead to?

Answer 10

○ Deamination of A gives hypoxanthine. pairs with C not T
○ Deamination of C gives uracil, pairs with A not G
○ Demainination of G gives xanthine, blocks DNA replication
○ T cannot be deaminated as it does not contain an amine group

Question 11

What are alkylating agents?

Answer 11

○ Add alkyl groups e.g. EMS
○ Cause transition mutation
○ Adding alkyl to G makes it pair with T

Question 12

What are intercalating agents?

Answer 12

○ Insert between base pairs e.g. ethidium bromide
○ Ethidium bromide used to visualise DNA
○ Causes insertion mutations (extra bases)

Question 13

What does UV radiation cause?

Answer 13

○ Base dimerisation and photoproducts
○ Causes bases to interact with themselves
○ Difficult to repair as we do not have an enzyme to efficiently repair

Question 14

What does heat cause?

Answer 14

○ Detachment of bases and gives rise to an AP site
○ AP site = apurinic or apyrimidinic
○ Easy to repair