Introduction to DNA replication

Question 1

Describe the relationship between the partner strands of DNA in a double helix.

Answer 1

A strand is exactly complementary to the nucleotide sequence of it’s partner strand

Question 2

In general what happens to the DNA in replication?

Answer 2

The 2 strands separate

Each strand acts as a template for the production of a new complementary strand

Question 3

DNA replication is semi-conservative, what does this mean?

Answer 3

Each of the 2 daughter molecule will have one of the old parent strands and 1 newly made strand

Question 4

What is the referred to as the replication machine?

Answer 4

The group of proteins and enzymes that carry out DNA replication

Question 5

When during the cell cycle does replication take place?

Answer 5

In the S phase of the cycle

Before mitosis

Question 6

Each new double strand consists of one parental strand and one new daughter strand, what is this known as?

Answer 6

Semiconservative replication

Question 7

What must first be done to DNA before replication can occur?

Answer 7

Helix must be opened to expose the separate strands

Question 8

What starts the process of DNA replication?

Answer 8

Initiator proteins start the process

Question 9

What do initiator proteins do?

Answer 9

They bind to DNA strands, pry them apart and break the hydrogen bonds

Question 10

What is the position where the DNA helix is first opened?

Answer 10

The Origin of Replication

Question 11

What is the Origin of Replication?

Answer 11

The position in DNA where the helix is first opened

Question 12

What is a replication “bubble”?

Answer 12

Where the two separate strands open up from the origin of replication

Question 13

What direction does replication occur in?

Answer 13

Replication proceeds in both directions from each origin until entire molecule is copied

Question 14

How many origins does a human genome have?

Answer 14

10,000 origins

Question 15

How many origins does a bacterial genome have?

Answer 15

1

Question 16

What is found at each end of a replication bubble?

Answer 16

A replication fork

Question 17

What is a replication fork?

2

Answer 17

A Y-shaped region found at each end of a replication bubble

This is where the new strands of DNA are elongating

Question 18

How do the replication forks move?

Answer 18

2 forks move away from the origin in either directions

Question 19

DNA replication occurs in two directions, what is this called?

Answer 19

Bidirectional

Question 20

What catalyses the elongation of a new strand of DNA at a replication fork?

Answer 20

DNA polymerases

Question 21

How many polymerases do eukaryotes use?

Answer 21

At least 11

Question 22

How many polymerases do prokaryotes use?

Answer 22

2, Pol 1 and pol II

Question 23

What do polymerases do?

Answer 23

Catalyse the elongation of a new strand of DNA at the replication fork

Question 24

What end of the DNA are nucleotides added onto?

Answer 24

The 3 prime end of the new strand

Question 25

What direction does DNA polymerase work in?

Answer 25

The 5’ to the 3’ direction

Question 26

What direction can DNA elongate in?

Answer 26

5’ to 3’

Starts at 5’
Works towards 3’
New nts added to 3’ end

Question 27

What is the leading strand?

2

Answer 27

The new strand in the 5’ to 3’ direction strand (complementary to the 3’ to 5’ parent strand)

The strand that can be synthesised continuously

Question 28

How is the lagging strand synthesised?

Answer 28

Synthesised discontinuously as a series of Okazaki fragments

Question 29

What joins the Okazaki fragments together?

Answer 29

DNA ligase

Question 30

What does DNA ligase do?

Answer 30

Joins the sugar-phosphate backbones of the Okazaki fragments together

Question 31

What direction is the leading strand replicated in relation to the replication fork?

Answer 31

Replicated in 5’ to 3’ direction

5’ at origin towards 3’ of fork

Adding on nts at the 3’ end of new strand continuously