DNA Replication

Question 1

What is DNA replication?

Answer 1

A semi-conservative process in which each parental strand serves as a template for the synthesis of a new complementary strand

Question 2

What are the 3 phases of DNA replication?

Answer 2

a) Initiation, b) Elongation and c) Termination.

Question 3

What happens in the initiation phase of DNA replication?

Answer 3

• DNA replication initiates at the origins of replication recognised by the origins recognition complex (ORC). —–Topoisomerases create a nick in a single DNA strand to be unwound by Helicases.
• This releases the tension holding the DNA helix in coils and supercoils and allows the double helix 3’ end of the RNA primers followed by the Polymerase.

Question 4

What happens in the elongation phase of DNA replication?

Answer 4

-Primers are removed and replaced with new DNA nucleotides and the backbone is sealed by DNA ligase. –The two replication forks are created to allow the replicative Polymerase to move to opposite directions.

Question 5

Which direction does polymerase move from on the leading strand?

Answer 5

On the leading strand polymerase (mainly DNA polymerase ε (epsilon)) moves continuously from
5’ > 3’

Question 6

How does polymerase elongate DNA on the lagging strand?

Answer 6

On the lagging strand Polymerase (mainly DNA polymerase δ (delta)) elongates a short stretch of DNA and then moves to a new primer while the helicase moves along the DNA. Synthesis is discontinuous.

Question 7

What is an Okazaki fragment?

Answer 7

A short fragment of DNA synthesised (in elongation phase) when polymerase elongates a short stretch of DNA and then moves to a new primer while the helicase moves along the DNA. Synthesis is discontinuous.