DNA replication in Eukaryotes

Question 1

What is the function of telomeres?

Answer 1

Protects the ends of DNA

Question 2

What is a chromatid?

Answer 2

Newly copied chromosome paired with the original chromosome

Question 3

What is the function of the centromere?

Answer 3

Promotes microtuble attachment during mitotic chromosome segregation

Question 4

What kind of proteins are histones?

Answer 4

Highly basic

Question 5

How many subunits is a histone protein made up of?

Answer 5

8

Question 6

What is a nucleosome?

Answer 6

A segment of DNA wrapped around a histone complex

Question 7

What is the effect of heterochromatin on gene expression?

Answer 7

Reduces gene expression

Question 8

What is the effect of euchromatin on gene expression?

Answer 8

Increases gene expression

Question 9

What is the effect of acetylation of chromatin on gene expression?

Answer 9

Produces euchromatin which Increases gene expression

Question 10

How are pre-mRNA introns removed?

Answer 10

By splicing involving the spliceosome

Question 11

What does initiation require?

Answer 11

An RNA primer

Question 12

Compare eukaryotic and prokaryotic origins of replication

Answer 12

• Prokaryotes have a single origin of replication site
• Eukaryotes have many origins of replication

Question 13

What is the function of topoisomerase I and II in eukaryotic DNA replication?

Answer 13

Relieves torsional stress ahead of the fork

Question 14

What is the function of single-stranded DNA binding proteins in eukaryotic DNA replication?

Answer 14

Stabilise the fork

Question 15

Which enzyme is responsible for lagging strand elongation in eukaryotic DNA replication?

Answer 15

DNA polymerase delta

Question 16

Which enzyme is responsible for leading strand elongation in eukaryotic DNA replication?

Answer 16

DNA polymerase epsilon

Question 17

Which enzyme is responsible for synthesis of okazaki fragments?

Answer 17

DNA polymerase alpha complexed with primase

Question 18

What is processivity?

Answer 18

The ability of DNA polymerase to continuously synthesise DNA without frequent dissociation from template

Question 19

Which type of DNA polymerase lack proofreading?

Answer 19

Alpha

Question 20

What is the function of the RFC clamp loader?

Answer 20

Recruits PCNA clamp at the junction between RNA/DNA primer and template

Question 21

What is the function of the PCNA clamp?

Answer 21

Forms a ring which displaces DNA polymerase alpha and recruits DNA polymerase delta and epsilon

Question 22

Outline how RNA primers are removed on the lagging strand

Answer 22

• DNA polymerase delta elongates Okazaki fragments
• When polymerase delta encounters an RNA primer it is pushed aside to form a flap
• FEN1 cuts flap at branch point
• DNA ligase I seals gap

Question 23

What is the function of FEN1?

Answer 23

It is an endonuclease involved in the removal of DNA primers

Question 24

What is the problem with synthesising DNA at the telomeric ends of lagging strand?

Answer 24

At the lagging strand, unable to add or remove RNA primers at telomeric ends

Question 25

What is the relationship between Chromosome length and replication?

Answer 25

Chromosome ends shorten after each round of replication

Question 26

What are the 2 parts of telomerase?

Answer 26

1. RNA template complementary to telomeric sequence
2. Reverse transcriptase

Question 27

What is the repeated sequence at telomeric ends?

Answer 27

TTAGGG

Question 28

What is the link between telomerase and cancer?

Answer 28

Telomerase is often reactivated in human cancers

Question 29

In what kind of cells is telomerase:

a) inactive
b) active?

Answer 29

a) Somatic cells
b) Stem cells

Question 30

How many RNA polymerases do eukaryotes have?

Answer 30

3

Question 31

At which point in the cell cycle does DNA replication occur?

Answer 31

S phase