DNA Replication

Question 1

What is the Central Dogma of DNA?

Answer 1

The central dogma of molecular biology deals with the transfer of sequential information.

DNA is replicated
DNA is transcribed to produce RNA.
RNA is translated to produce Proteins.

Question 2

What is the general structure of DNA?

Answer 2

DNA is made of two linked strands - a shape known as a double helix. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T).

Question 3

How many models of DNA replication were proposed?

Answer 3

3

Question 4

What are the three DNA replication models?

Answer 4

Conservative, Semi-conservative and Dispersive

Question 5

What is the Origin of Replication (oriC)?

Answer 5

The origin of replication (oriC) is the site at which replication is initiated.

Question 6

What happens at the Origin of Replication?

Answer 6

The pre-replication complex binds and begins the process of replication.

DnaA proteins bind to the oriC and cause the region to unwind as the strands stick to the DnaA proteins

This causes the A-T-rich region to the left to separate.

Helicase enzymes (DnaB) then bind and ‘unzip’ the rest of the strand forming the replication

Question 7

What are Topoisomerases?

Answer 7

Topoisomerases are enzymes that accomplish this feat:

• Topoisomerase I nicks DNA on one strand to relieve tension
• Topoisomerase II (a.k.a. DNA gyrase) cuts double-stranded DNA and then rejoins it to relieve tension.

Question 8

How many enzymes are needed to allow the synthesis of a complementary strand?

Answer 8

Three

Question 9

What are the three enzymes needed to allow the synthesis of a complementary strand?

Answer 9

Single-strand binding proteins, Primase and DNA Polymerase III

Question 10

What is the function of Single-strand binding proteins?

Answer 10

Stabilise the single-stranded DNA and stop the strands from sticking back together.

Question 11

What is the function of Primase?

Answer 11

Primes new strand of DNA

Question 12

What is the function of DNA Polymerase III?

Answer 12

Synthesises new DNA strand

Question 13

How does DNA Polymerase III synthesise DNA?

Answer 13

Synthesises DNA (5’ to 3’) using a DNA template (3’ to 5’)

Question 14

Can DNA synthesis happen without a primer?

Answer 14

No

Question 15

Why does DNA synthesis require a primer?

Answer 15

The RNA primer provides a 3’ OH group which allows chain extension

Question 15

Why does DNA synthesis require a primer?

Answer 15

The RNA primer provides a 3’ OH group which allows chain extension

Question 16

Can DNA be synthesised in both directions?

Answer 16

No, DNA can only be synthesised in the 5’ – 3’ direction

Question 17

What is a leading strand?

Answer 17

Continuous DNA synthesis in the same direction as the replication fork movement

Question 18

What is a lagging strand?

Answer 18

Discontinuous DNA synthesis in the opposing direction to the replication fork movement

Question 19

What does DNA Polymerase I do after the synthesis with a primer?

Answer 19

DNA polymerase I has an exonuclease activity that removes the RNA primer and replaces the ‘gap’ with DNA

Question 19

What does DNA Polymerase I do after the synthesis with a primer?

Answer 19

DNA polymerase I has an exonuclease activity that removes the RNA primer and replaces the ‘gap’ with DNA