NAGE 2

Question 1

First step of DNA replication

Answer 1

DNA helicase to unwind DNA

Uses ATP to break hydrogen bonds

Question 2

Second step of DNA replication

Answer 2

DNA Polymerase adds new nucleotides to 3’ end.

Requires a free 3’ OH group and energy which is supplied by the hydrolysis of triphosphates on the dNTPs

Question 3

What are the requirements of DNA Polymerase?

Answer 3

Template strand
supply of dNTPs
Oligonucleotide primer

Question 4

What is an origin of replication?

Answer 4

Discrete points on DNA where replication begins

Question 5

What is a replication fork?

Answer 5

site of DNA synthesis

Question 6

What is the difference between the leading strand and the lagging strand?

Answer 6

The leading strand is synthesised continuously whereas the lagging strand is synthesised in Okazaki fragments. The leading strand only requires 1 RNA primer whereas the lagging strand requires a new primer for each Okazaki fragment

Question 7

Describe the oligonucleotide primer

Answer 7

an RNA primer
synthesised by DNA primase - an RNA polymerase
around 10 nucleotides in length and transient

Question 8

What happens to the primer in the end?

Answer 8

The primer is erased by a ribonuclease using 5’ to 3’ exonuclease activity,
it is then replaced with DNA by a repair DNA polymerase
Then the fragments of DNA are joined together using DNA ligase. This is an active process using ATP.

Question 9

Describe the replication fork proteins

Answer 9

Sliding clamp protein - prevents DNA polymerase from falling off DNA

Single strand DNA binding protein - prevents the formation of secondary structures

Question 10

Describe the proof-reading mechanism of DNA Polymerase

Answer 10

DNa polymerase checks that the current base pair is correct before moving onto the next one. Incorrect base pairs are removed using the 3’-5’ exonuclease activity of DNA polymerase`

Question 11

Summarise the replication of a eukaryotic genome

Answer 11

Multiple replication forks dispersed at intervals of 100kbp. Form bi-directional replication forks. Replication is completed when all the forks meet up.

Question 12

Summarise the replication of a prokaryotic genome

Answer 12

begins at origin of replication called Ori C., Forms 2 replication forks proceeding in opposite directions which eventually meet at the other side of the circular chromosome

Question 13

Give the timings for each stage of the cell cycle

Answer 13

M - 1 hour
G1 - 10 hours
S - 9 hours
G2 - 4 hours