Lecture 5 DNA Replication I

Question 1

How can DNA replication be visualized

Answer 1

By use of modified nucleotides, which can be radioactively labelled, so that they fluoresce under UV light, allowing DNA to be visualized.

Question 2

When new DNA strands are synthesized at the replication fork, this process is known as….?

Answer 2

DNA dependant DNA synthesis, because DNA is the template.

Question 3

In which direction does DNA synthesis always occur?

Answer 3

5’ to 3’ direction.

Question 4

Which enzyme is responsible for DNA dependant DNA synthesis

Answer 4

DNA dependent DNA polymerase.

Question 5

What are the names of the DNA polymerases in bacteria

Answer 5

DNA polymerase I

DNA polmyerase III

Question 6

Which is the main replicating enzyme in bacteria

Answer 6

DNA polymerase III

Question 7

DNA polymerase III has which exonuclease activity

Answer 7

Has 3’5’ exonuclease activity only

Question 8

DNA polymerase I has which exonuclease activity

Answer 8

Has both 3’5’ and 5’3’ exonuclease activity

Question 9

What are the names of the replicating polymerases in eukaryotes

Answer 9

DNA polymerase alpha

DNA polymerase delta

Question 10

Which is the main replicating enzyme in eukaryotes

Answer 10

DNA polymerase delta

Question 11

dna polymerase alpha has which activity

Answer 11

neither 3’5’ or 5’3’ exonuclease activity

Question 12

dna polymerase delta has which activity

Answer 12

has 3’5’ exonuclease activity only.

Question 13

What is required for DNA synthesis in bacteria

Answer 13

a Primer made from RNA.

Question 14

How are primers produced in bacteria

Answer 14

Primase enzyme synthesises them.

Question 15

In bacteria, how is the leading strand synthesized

Answer 15

RNA primer binds first. DNA polymerase III continues to synthesize the rest of the new strand.

Question 16

In eukaryotes, how is the leading strand synthesized

Answer 16

• RNA Primer binds.
• DNA pol alpha extends primer and adds the first 15-20 nucleotides.
• DNA polymerase delta continues to synthesize the rest of the strand.

Question 17

In which direction does DNA synthesis always take place

Answer 17

5’3’ direction.

Question 18

The leading strand ….

Answer 18

Can be copied by continuous DNA synthesis.

copying of leading strand requires an RNA primer.

Question 19

What is a key feature held by most DNA polymerases

Answer 19

• Most can also degrade DNA

- This is called exonuclease activity.

Question 20

What are the two types of Exonuclease activity that DNA polymerases have

Answer 20

3’5’ exonuclease activity (proofreading)

5’3’ exonuclease activity

Question 21

Explain what is meant by 3’5’ Exonuclease activity

Answer 21

• proofreading ability
• polymerase can remove nucleotides it has just inserted.
• allows errors to be corrected.

Question 22

Explain what is meany by 5’3’ exonuclease activity

Answer 22

• polymerase can remove DNA already attached to the template.

Question 23

What are the roles of Single strand binding proteins

Answer 23

• to prevent the seperated strands from re-attatching

- to protect strands from exonuclease activity.

Question 24

Name an example of a single strand binding protein in Eukaryotes.

Answer 24

Replication protein A

Question 25

State the functions and structure of DNA polymerase I and III in bacteria

Answer 25

polymerase I is responsible for repair

pol III is the main replicating enzyme

Question 26

State the functions and structure of DNA Polymerase alpha and delta in eukaryotes

Answer 26

Pol alpha is

Pol delta is the main replicating enzyme