L7: DNA Replication

Question 1

Why is DNA replication important?

Answer 1

New cells are created by mitosis, which required DNA replication

Question 2

What happens in DNA replication?

Answer 2

Identical copy of the parent DNA is used as a template for a new strand

Question 3

Define semi-conservative replication

Answer 3

2 copies of the original DNA is produced, consisting of only half of the material

Question 4

When is the replication fork created?

Answer 4

DNA helicase unwinds the double helix structure

Question 5

Initiation of DNA replication in prokaryotes

Answer 5

1) Initiation proteins bind to replication origin
2) Separate strands of DNA
3) Two ‘replication forks’ are formed

Question 6

Which directions do replication forks move?

Answer 6

In opposite directions

Question 7

Which bonds are nucleotides joined by?

Answer 7

Phosphodiester Bonds

Question 8

Structure of deoxynucleoside triphosphates (dNTPs)

Answer 8

3 phosphate groups attached to the 5’ carbon of deoxyribose

Question 9

Role of DNA polymerase III

Answer 9

Synthesis the bulk of DNA in E.coli

Question 10

What is a holoenzyme?

Answer 10

Composed of multiple subunits with different functions

Question 11

What does DNA pol III require for DNA synthesis?

Answer 11

RNA primer

Question 12

How is RNA primer created ?

Answer 12

Using enzyme PRIMASE

Question 13

Which direction does DNA pol III synthesis new DNA in?

Answer 13

5’ to 3’ direction

Question 14

What is the leading strand?

Answer 14

Replicates continuously

Question 15

What is the lagging strand?

Answer 15

Replicates to form short fragments

Question 16

Polarity problem in DNA replication

Answer 16

DNA double helix have opposite polarity but all DNA polymerase replicate in the same direction

Question 17

What are Okazaki fragments joined by?

Answer 17

DNA ligase

Question 18

Role of ligase in DNA replication

Answer 18

Joins Okazaki fragments into continuous DNA strands

Question 19

Function of enzyme topoisomerase

Answer 19

Preventing DNA from getting tangled
- Relieving pressure supercoiling ahead of replication fork

Question 20

Role of Type I topoisomerases

Answer 20

Cut 1 DNA strand

Question 21

Role of Type II topoisomerases

Answer 21

Cut both DNA strands, pass coil through gaps (ATP) & reseal the strands

Question 22

Role of helicase in DNA replication

Answer 22

Separates DNA strands

Question 23

Role of single-stranded binding protein in DNA replication

Answer 23

Prevents DNA strands from re-annealing

Question 24

Role of primase in DNA replication

Answer 24

Synthesise RNA primers

Question 25

Role of DNA polymerase III

Answer 25

Synthesise bulk of DNA

Question 26

Role of sliding clamp in DNA replication

Answer 26

Keeps DNA pol III firmly attached to DNA

Question 27

What enzymes act as proofreaders during DNA polymerisation in DNA replication?

Answer 27

Exonucleases

Question 28

How does the exonuclease activity proofread?

Answer 28

Remove last added nucleotide via exonuclease activity, then insert the correct nucleotide

Question 29

Which DNA polymerase has exonuclease activity?

Answer 29

DNA polymerase I and III

Question 30

What is a mismatch repair?

Answer 30

Errors missed by proofreading activity, corrected by repair machinery

Question 31

How does the mismatch repair work?

Answer 31

1) Identify incorrect base pairs
2) Remove DNA in new strand
3) Synthesise replacement DNA

Question 32

What is DNA replication in eukaryotic cells?

Answer 32

Part of the ‘cell cycle’

Question 33

Where is DNA replication in eukaryotic cells

Answer 33

Nucleus

Question 34

Where is DNA replication in prokaryotic cells?

Answer 34

Cytoplasm