DNA Replication

Question 1

Helicase is loaded by?

Answer 1

Initiator protein

Question 2

F(n) of helicase

Answer 2

Unwinds double helix;

Unzips two parental strands;

Disrupting H bonds

Question 3

How is the stability of replication fork maintained?

Answer 3

Single strand binding DNA protein;

Keep the strand from reannealing

Question 4

Fn of topoisomerase

Answer 4

Relieve strain by creating a temporary break in the sugar phosphate backbone;

Free rotation;

Allow unwinding of double helix of replication fork

Question 5

DNA primase?

Answer 5

Adds RNA primer;

Provides free 3’OH end;

DNA polymerase initiate DNA synthesis

Question 6

Fn of DNA polymerase

Answer 6

Selects free dNTPs complementary to those on parental strand;

5’-> 3’

Question 7

Explain proof reading mechanism

Answer 7

Incorrect deoxyribonucleotide added;

Remove by 3’->5’ exonuclease activity of DNA polymerase;

Replaced with the correct one

Question 8

Leading strand

Answer 8

Synthesised continuously;

As a single polynucleotide;

5’->3’ directions;

Towards replication fork

Question 9

Lagging strand

Answer 9

Discontinuously;

Away from replication fork

Question 10

How to px continuous strand from lagging strand

Answer 10

Many Okazaki fragments;

Another DNA polymerase removes RNA primer;

Replaces with DNA;

DNA ligase catalysed the formation of phosphodiester bond

Question 11

How end replication problem arises?

Answer 11

Removal of last RNA primers at 5’ends of new Daughter strands;

Leaving ss parental DNA an overhang extending beyond 5’ end;

DNA polymerase cannot fill in the overhang;

No free 3’ -OH end