Nucleic Acids

Question 1

Outline the process of semi-conservative replication [6]

Answer 1

1) DNA Helicase breaks down hydrogen bonds between complementary bases.
2) The double helix separates and unwinds into 2 separate strands.
3) Each exposed nucleotide acts as a template strand and free nucleotides attach to bases on old strands by complementary base pairing.
4) Hydrogen bonds form between complementary bases.
5) DNA Polymerase joins the new nucleotides together by phosphodiester bonds in a condensation reaction.
6) DNA Ligase winds the strands up to form 2 double helices
The 2 new DNA molecules are identical to the old molecule, and contain one old strand and one new.

Question 2

Why did many scientists doubt the fact that DNA carried the genetic code?

Answer 2

Due to its relative simplicity

Question 3

Why is semi-conservative replication called this?

Answer 3

• Half of the old DNA molecule is conserved in each new DNA strand formed

Question 4

Why is it important to retain 1 original DNA strand?

Answer 4

• Ensures genetic continuity between generations of cells
• New cells will inherit all their genes from their parent cells
• Mutations are less likely to occur
• Cells are being constantly replaced and new cells must perform the same functions as the old ones

Question 5

When does DNA replication happen?

Answer 5

During the S phase of interphase (in preparation for mitosis)

Question 6

Why does DNA replication happen?

Answer 6

So that the new daughter cells produced will both receive the full copies of the parental DNA