SSB + BER1

Question 1

What are the 4 different types of base damage?

Answer 1

• Substitution
• Alkylation - adding a methyl group
• Loss - losing a base due to natural hydrolysis
• Oxidation - via peroxides

Question 2

What are the 2 different types of sugar damage?

Answer 2

• Hydrogen abstraction

- Oxidation

Question 3

What is deamination and when does it happen?

Answer 3

• Loss an amino group

- Happens during base substitution

Question 4

What is the product of the deamination of 5-methyl cytosine?

Answer 4

Thymine

Question 5

What is the product of the deamination of Adenine?

Answer 5

Hypoxanthine

Question 6

What is the product of the deamination of Cytosine?

Answer 6

Uracil

Question 7

What is the product of the deamination of Guanine?

Answer 7

Xanthine

Question 8

Which 4 bases are similar to each-other in base substitution?

Answer 8

• Thymine is similar to uracil

- Guanine is similar to hypoxanthine

Question 9

Explain the term ‘pre-mutagenic’

Answer 9

• When there is DNA damage, it needs to be recognised
• If the cell goes into S phase before the damage is recognised, it is read as NORMAL
• This is pre-mutagenic, which can be fixed before the next cell cycle.

Question 10

What is a point mutation?

Answer 10

When the cell does not fix the pre-mutagenic base and it continues onto the next cell cycle as if it is not there.

Question 11

Which bases are pyrimidines?

Answer 11

Thymine and Cytosine

Question 12

Which bases are purines?

Answer 12

Guanine and Adenine

Question 13

What is a transverse mutation?

Answer 13

Purine –> Pyrimidine

Pyrimidine –> Purine

Question 14

What is a transition mutation?

Answer 14

Purine –> Purine

Pyrimidine –> Pyrimidine

Question 15

What are the 3 most common positions of base alkylation?

Answer 15

• N7MG
• O6MG
• N3MA

Question 16

What is monofunctional alkylation?

Answer 16

When damage is caused in one nucleophilic centre in DNA.

Question 17

Describe spontaneous alkylation

Answer 17

• When S-Adenosyl Methionine (SAM) forms O6MG
• O6MG looks like Adenine
• Therefore it mismatches with Thymine
• This is a transition mutation

Question 18

What is induced alkylation caused by?

Answer 18

Caused by carcinogens found in:

• Tobacco
• Overcooked meat
• Car Exhaust fumes

Question 19

Describe spontaneous base loss

Answer 19

• Caused by the hydrolysis of the N-Glycosyl bond between the sugar and the base
• Causing depurination and depyrimidation

Question 20

What is induced base loss caused by?

Answer 20

Environmental alkylation agents such as:

• Aflatoxin
• BPDE

Question 21

What is spontaneous base oxidation caused by?

Answer 21

Cellular metabolites such as ROS.

Question 22

What is induced base oxidation caused by?

Answer 22

• X-Rays
• Cosmic radiation
• Radon

Question 23

Give an example of a base oxidation scenario

Answer 23

1. Guanine + Oxidation = 8 Hydroxy-Guanine (8HG)
2. 8HG is similar to Thymine, therefore Adenine is paired with it = Pre- Mutagenic
3. Another round of replication occurs forming T:A T:A base pairs because it thinks the 8HG is a Thymine so it keeps replicating Thymine.
4. The 8HG is completely missed = Mutation.