DNA Synthesis

Question 1

What does it mean by semi-conservative replication?

Answer 1

Each daughter DNA has one parent strand and one new strand

Question 2

Where is DNA replication initiated?

Answer 2

• at specific sites called replication origins
• replication origins are recognised by an initiation complex
• DNA at these origins unwinds to form a replication bubble and allows access to replication machinery

Question 3

What is the function of DNA polymerase?

Answer 3

• synthesis of DNA
• requires a template and building blocks
• copies one of the parental strands
• requires RNA/DNA that acts as a primer and magnesium ions
• acts in the 5’ to 3’ direction
• utilises complementary base-pairing to synthesise new DNA strand
• has a proof-reading/editing function

Question 4

How does DNA polymerase use primers?

Answer 4

• primers provide a 3’ OH end
• DNA polymerase uses primer and complementary base
• adds free-floating nucleotide to OH
• OH makes a covalent bond with the phosphate
• formation of phophodiester bond= loss of two phosphates, enzyme prevents it from going backwards

Question 5

What is the function of DNA helicase?

Answer 5

Breaks hydrogen bonds between the two strands

Question 6

What is the function of DNA binding proteins?

Answer 6

Binds to strand of DNA to prevent it from degrading

Question 7

What is the function of primase?

Answer 7

Lays down a small RNA strand complementary to strand

Question 8

What is the function of replicative DNA polymerase?

Answer 8

Extends short RNA primer

Question 9

What is the function of repair DNA polymerase?

Answer 9

Replaces RNA with DNA

Question 10

What is the function of DNA ligase?

Answer 10

Links phosphates together to make the continuous strand

Question 11

What is the function of topoisomerases?

Answer 11

Breaks and rejoins DNA strands and allows release of positive supercoils

Question 12

Why is there a low error rate during DNA replication?

Answer 12

• proof-reading/editing and base pairing by DNA polymerase

- mismatch repair system corrects most of polynmerase errors

Question 13

What do inherited defects in mistmatched repair genes cause?

Answer 13

• cause cancer

- MutS recognises mismatch and MutH and MutL correct the error

Question 14

Give examples of different DNA replication inhibitors

Answer 14

Antibacterial:
-gyrase inhibitors
Antitumour:
-topo II inhibitors
Antiviral agents:
-reverse transcriptase