DNA replication

Question 1

What is DNA replication?

Answer 1

The process whereby DNA makes a copy of itself during cell division

Question 2

When does DNA replication occur?

Answer 2

During cell division

Question 3

What does Helicase do?

Answer 3

unzips the double helix, disrupting hydrogen bonds between bases to separate DNA strands

Question 4

What does Topoisomerase do?

Answer 4

Breaks, untwists and reconnects DNA ahead of Helicase to relieve torsional strain in DNA

Question 5

What does primase do?

Answer 5

Anneals RNA primers to specific locations in the DNA strand to kick-start replication

Question 6

What does DNA polymerase III do?

Answer 6

Generates new complimentary strand by adding nucleotides to the new chain during elongation

Question 7

Which end does the DNA polymerase add nucleotides to?

Answer 7

3’ end

Question 8

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

Answer 8

The leading strand only needs one primer as it continuously synthesises proteins on the complementary strand

The lagging strand is synthesised in Okazaki fragments that each require a primer to initiate synthesis

Question 9

What does DNA Polymerase I do?

Answer 9

Swaps primer nucleotides for appropriate DNA nucleotides

Question 10

What does ligase do?

Answer 10

Makes sure all nucleotides are reconnected after replication

Question 11

What is proofreading and why is it needed?

Answer 11

when enzymes backtrack on the newly synthesised DNA strand to correct any errors

Question 12

What is the name of the process when enzymes swap out incorrect bases for the correct ones?

Answer 12

Mismatch repairs

Question 13

What are mismatch repairs?

Answer 13

When special enzymes swap out incorrect bases for the correct ones to avoid mutation

Question 14

What is a replication fork?

Answer 14

the structure that forms when helicase unzips double helix, breaking the hydrogen bonds, resulting in two ‘prongs’ of DNA strands

Question 15

What is torsional strain and which enzyme prevents it?

Answer 15

Supercoiling of the DNA caused by helicase’s separation of the two strands.
It is prevented by topoisomerase

Question 16

What are the 4 main steps of DNA replication?

Answer 16

1) Replication fork formation (separating the two DNA strands)
2) Primer binding
3) Elongation
4) Termination

Question 17

What happens during the replication fork formation phase?

Answer 17

Helicase disrupts the bases’ hydrogen bonds to unzip the two strands of DNA

Question 18

What groups are attached to the 3’ and 5’ end of DNA?

Answer 18

the 5’ end has a phosphate group attached

the 3’ end has a hydroxyl (OH) group attached

Question 19

Which direction does DNA replication proceed in?

Answer 19

From 5’ to 3’

Question 20

What happens in the primer binding phase of DNA replication?

Answer 20

Primase binds primers to the 3’ end of the strands to indicate the start of replication

Question 21

What happens in the elongation phase of DNA replication?

Answer 21

DNA polymerase III binds to the primer site of the strand

Adds new nucleotide complementary base pairs to the strand

Question 22

What happens during the Termination phase of DNA replication?

Answer 22

DNA polymerase I swaps primer nucleotides for appropriate DNA nucleotides

DNA is proofread

DNA ligase joins okazaki fragments together to make sure all strands are joined

The two new identical strands are formed

Question 23

What type of bond joins the new nucleotide to the complementary strand?

Answer 23

a phosphodiester bond