DNA Replication

Question 1

Describe the process of DNA Replication

Answer 1

1) DNA strands run anti-parallel to one another
2) The enzyme Helicase unwinds the DNA double helix
3) DNA polymerase attaches to the ‘leading’ strand
4) DNA polymerase synthesises a new DNA strand in the 5’ to 3’ direction
5) Another DNA polymerase molecule attaches to the ‘lagging’ strand
6) DNA is synthesised in the 5’ to 3’ direction
7) Helicase continues to unwind the DNA double helix
8) Continuous synthesis proceeds on the ‘leading’ strand
9) DNA polymerase detaches from the ‘lagging’ strand, and rejoins further down
10) Synthesis of DNA continues on the ‘lagging strand’
11) DNA polymerase is unable to join up the fragments on the lagging strand
12) This is done by the enzyme Ligase

Question 2

Describe the process of semi-conservative DNA replication

Answer 2

• DNA Helicase breaks the hydrogen bonds joining the complementary base-pairs of the parent strand, forming 2 template strands.
• Free nucleotides bind to their specific base pairs on each template strand.
• DNA Polymerase joins the free nucleotides by forming phosphodiester bonds.