2 - DNA replication, cell cycle & mitosis

Question 1

What is semi-conservative DNA replication?

Answer 1

Each strand forms the template for a new strand of DNA.

Question 2

DNA replication requires..

Answer 2

Template stand.
Oligonucleotide primer.
Supply of dNTPs.

Question 3

DNA helicase does what?

Answer 3

Energy from ATP is used to break H bonds in DNA to separate strands.

Question 4

DNA polymerase does what?

Answer 4

Add deoxynucleotide tri-phosphates (dNTPs) to the 3’ end of a DNA molecule.

Question 5

DNA synthesis goes in what direction?

Answer 5

5’ - 3’ direction

Question 6

What drives the reaction?

Answer 6

The release of energy from the hydrolysis of the tri-phosphate.

Question 7

Drugs used as chain terminators are called?

Answer 7

Nucleoside analogs. (No -OH group on carbon 3 so no nucleotides can be added).

Question 8

Name 4 nucleoside analogs

Answer 8

ddC - H on C3
AZT - N3 on C3
Acyclovir - Guanine base
Cytosine arabinose - Chemotherapy drug

Question 9

What is the origin of replication?

Answer 9

Discrete points on the DNA molecule where replication begins.

Question 10

What direction are strands synthesised in what direction?

Answer 10

5 to 3.

Question 11

What is the replication fork?

Answer 11

The site of DNA synthesis, it moves along during the process.

Question 12

How is the leading strand synthesised?

Answer 12

Continuously in 5 - 3 direction.

Question 13

How is the lagging strand synthesised?

Answer 13

Discontinuously in 5 - 3 direction, making okazaki fragments.

Question 14

How is a new chain started?

Answer 14

An RNA primer

Question 15

How is an RNA primer made?

Answer 15

Synthesised by an RNA polymerase called primase.
About 10 bases long
The primer is extended by a DNA Polymerase until the last RNA primer is reached.
Its removed later.

Question 16

How is the RNA primer used on the leading strand?

Answer 16

Only 1 is required, at the replication origin.

Question 17

How are okazaki fragments joined?

Answer 17

1. Primer is removed
2. DNA polymerase then synthesises DNA through the RNA primer region. (Repair DNA polymerase)
3. Two adjacent strands of DNA are joined together.

Question 18

How is the RNA primer removed?

Answer 18

A ribonuclease removes the RNA primer using a 5′ to 3′ exonuclease activity.

Question 19

How are the 2 adjacent strands joined together?

Answer 19

DNA ligase joins them using ATP.

Question 20

What is a sliding clamp?

Answer 20

Makes sure DNA polymerase doesn’t fall off DNA strand.

Question 21

What does a single strand DNA binding protein do?

Answer 21

Make sure no H bonds are reformed.

Question 22

How accurate is DNA replication?

Answer 22

1 error per 10^9 base pairs.

Question 23

How is DNA proof read?

Answer 23

DNA Polymerase has 3’ to 5’ exonuclease activities for proof reading.

Question 24

Replication of E.coli genome.

Answer 24

1. There is only 1 origin called Ori C.
2. There are 2 replication forks in opposite directions.
3. They move in opposite directions and meet at the other side of the circular chromosome.
   This is called Bi-directional replication.

Question 25

Structure of eukaryotic chromosomes?

Answer 25

Linear and long

Question 26

How far are replication forks spread out?

Answer 26

100kb pairs apart.

Question 27

Replication of eukaryotic genome?

Answer 27

Each replication origin gives bidirectional replication forks.
Replication is finished when all the forks have met.

Question 28

What are the Mammalian Cell cycle stages?

Answer 28

Interphase…
G1 - Gap phase 1
10 hours, DNA of each chromosome is a single, linear double helix of DNA.

S1 - Synthesis 1
9 hours, DNA replication.

G2 - Gap 2
4 hours, each chromosome has 2 identical sister chromatids.

Mitosis…
1 hour, the 2 chromatids separate to the daughter cells.

(G0 happens after G1 for cells that have stopped dividing)

Question 29

6 Stages of mitosis?

Answer 29

Prophase - Chromatids condense
Metaphase - Line on central plane of spindle
Anaphase - Sister chromatids pulled to spindle poles
Telophase - Cell membrane reforms
Cytokinesis - 2 daughter cells & nucleus reforms.