DNA Replication

Question 1

What is DNA replication?

Answer 1

Mechanism by which DNA makes a copy of itself during cell division and proof-reads it to maintain fidelity

Question 2

What is the ‘replication factory’?

Answer 2

Many proteins and enzymes clustered together which work in a coordinated and cooperative manner to carry out DNA replication

Question 3

When does DNA replication occur in the cell cycle and how long does it take?

Answer 3

S phase

8-9 hours

Question 4

Why is DNA replication described as semi-conservative?

Answer 4

Daughter DNA helices formed each contain one of the parent strands

Question 5

In what direction does DNA polymerase synthesise DNA?

Answer 5

5’ to 3’

Question 6

Describe what DNA polymerase does.

Answer 6

Extends new strand of DNA by adding complementary dNTPs to the 3’ end of the sugar-phosphate backbone

Pyrophosphate is released

Question 7

What carries out proof-reading of the new DNA strand?

Answer 7

DNA polymerase - exonuclease 3’ to 5’ activity detects non-complementary nucleotide conformation

Question 8

Describe the structure and function of DNA helicase.

Answer 8

Made up of 6 proteins arranged in a ring shape

Unwinds DNA double helix by breaking hydrogen bonds

Question 9

What is the function of topoisomerase?

Answer 9

Releases supercoils in DNA

Question 10

What are SSBs?

Answer 10

Single strand binding proteins

Bind to SS DNA so it cannot anneal back together to increase efficiency of replication

Tetramer structure

Question 11

What is a primase?

Answer 11

RNA polymerase used to make short RNA primers

Question 12

What shape is DNA polymerase (III)?

Answer 12

Claw-shaped

Question 13

What is the function of a sliding clamp?

Answer 13

Helps DNA polymerase to hold onto the strand it is copying

Question 14

What does RNAse H do?

Answer 14

Removes RNA primers

Question 15

What does DNA ligase do?

Answer 15

Links DNA fragments together via phosphodiester bonds

Question 16

Where does replication start?

Answer 16

Origin of replication

Question 17

How many origins of replication does a bacterial chromosome have?

Answer 17

1

Question 18

How many origins of replication are there in a human cell?

Answer 18

50-100,000

Question 19

Where does DNA helicase work?

Answer 19

Replication fork

Question 20

What occurs at the replication fork?

Answer 20

Unwinding of DNA

SSBs coat SS DNA

Question 21

What are primers?

Answer 21

Short nucleic acid sequences which provide a starting point for DNA synthesis

Removed after DNA synthesis

Question 22

How long are primers?

Answer 22

~10 bases long

Question 23

What is discontinuous replication theory?

Answer 23

One strand (leading strand) is synthesised continuously

Other strand (lagging strand) is replicated in short “Okazaki” fragments ~1000 nucleotides long

These are ligated later after primers are removed

Question 24

How accurate is DNA polymerase?

Answer 24

~1 mistake per 1,000,000 nucleotides

Usually corrected by proof-reading activity

Question 25

Describe the process of DNA replication.

Answer 25

1. Helicases unwind parental double helix to form replication fork 2. SSBs stabilise unwound DNA 3. Leading strand synthesised continuously in 5' to 3' direction by DNA polymerase 4. Lagging strand is synthesised discontinously in Okazaki fragments 5. After RNA primers are removed and replace by DNA, DNA ligase joins Okazaki fragments