Chemical Mutagens

Question 1

Which base does 5-bromouracil substitute?

Answer 1

Thymine

Question 2

Which tautomeric forms can 5-bromouracil exist in?

Answer 2

Both keto and enol.

Question 3

HNO2 deaminates adenine to form which base, and which base does this new base pair with?

Answer 3

A -> hypoxanthine, which pairs to C.

Question 4

HNO2 deaminates cytosine to form which base, and which base does this new base pair with?

Answer 4

C -> U, which pairs to A.

Question 5

In terms of mutagenesis, what is the problem with deaminating C -> U?

Answer 5

Uracil is detected by repair systems are removed.

Question 6

What base does NH2OH modify, and what is this modified base called?

Answer 6

C -> N 4-hydroxycytosine

Question 7

What base does N 4-hydroxycytosine behave like?

Answer 7

Thymine

Question 8

NTG, EES, and EMS are examples of what agents?

Answer 8

Alkylating Agents

Question 9

What are the effects of alkylation on bases?

Answer 9

Changes in H-bonding patterns, mispairing, depurination.

Question 10

What effect do intercalating agents have on DNA?

Answer 10

They insert between DNA base adjacently.

Question 11

What effect on a reading frame does intercalation have?

Answer 11

Frameshift mutation (+1, sometimes +2)

Question 12

What causes the frameshift mutation?

Answer 12

DNA excision.

Question 13

What effect does UV light have on DNA?

Answer 13

It causes thymine dimer formation.

Question 14

What wavelength is the UV light?

Answer 14

260nm

Question 15

What is photoreactivation?

Answer 15

A visible light induced system that cleaves thymine dimers.

Question 16

What is Dark Repair?

Answer 16

A thymine dimer excision system.

Question 17

What are the Dark Repair gene products?

Answer 17

Uvr A,B,C

Question 18

Why is Dark Repair non error-prone?

Answer 18

The thymine-dimer is excised, and the strand is reformed from the template strand.

Question 19

When is SOS Repair activated? (In relation to thymine dimer repair)

Answer 19

When Dark Repair leaves residual DNA lesions.

Question 20

RecA catalyses the clevage of what protein?

Answer 20

LexA

Question 21

In the context of SOS repair, what is the function of LexA?

Answer 21

It represses SOS Repair.

Question 22

recA is switched on by the SOS Repair system. What mechanism does this activate?

Answer 22

A positive feedback mechanism - the clevage of LexA.

Question 23

What is the sfi gene?

Answer 23

Cell division inhibitor.

Question 24

What are the umuC,D genes?

Answer 24

Inducible error-prone repair genes.