DNA Structure & Replication

Question 1

What happens in semi-conservative replication

Answer 1

• for dna to replicate, the double helix structure had to unwind and then separate into two strands
  -> the hydrogen between the complementary bases must be broken
  -> free nucleotides will then pair with the exposed bases, and hydrogen bonds form between them
  -> the new nucleotides join to their adjacent nucleotides with phosphodiester bonds
  -> the 2 new molecules of DNA are produced

Question 2

What enzyme breaks the DNA strands apart

Answer 2

Helicase

Question 3

Enzymes used in DNA replication

Answer 3

• helicase
• polymerase

Question 4

What does DNA helicase do

Answer 4

Travels down the DNA backbone, catalysing the reaction that breaks the hydrogen bonds between complementary bases

Question 5

What does DNA polymerase do

Answer 5

Catalysed the formation of phosphodiester bonds between nucleotides being formed and the newly exposed bases

Question 6

How do mutations happen

Answer 6

• the sequence of bases doesn’t always go the way it’s supposed to
• these errors occur randomly and lead to a change in the sequence of bases
  -> mutation

Question 7

What is a degenerate code

Answer 7

There are more codons than amino acids so many amino acids are coded for more than one codon
-> due to this, code = degenerate

Question 8

DNA has 4 bases which means there are […] different combinations of codons possible

Answer 8

64

(4x4x4 bc it’s a triplet)

Question 9

The […] strand is synthesised discontinously

Answer 9

Lagging

Question 10

The leading strand of DNA can be replicated […]

Answer 10

Continuously

Question 11

What are okazaki fragments

Answer 11

The small sections that the lagging strand has to be synthesised discontinuouslg in the opposite direction

Question 12

What enzyme joins okazaki fragments together

Answer 12

DNA ligase

Question 13

DNA polymerase travels in what direction

Answer 13

3’ to 5’