DNA replication

Question 1

What type of replication does DNA use?

Answer 1

Semi conservative replication

Question 2

What does semi-conservative DNA do?

Answer 2

• preserves DNA for many generations as one old DNA strand acts as a template
• This means there is genetic continuity between generations

Question 3

What is step one of DNA replication?

Answer 3

• DNA helicase breaks the hydrogen bonds between complementary base pairs on the two polynucleotide strands
• This causes the double helix to unwind into two strands

Question 4

What is step two of DNA replication?

Answer 4

• Each single strand of the double helix now acts as a template for a new double helix
• Free-floating nucleotides bind to the exposed complementary base pairings on each single strand
• A & T and C & G

Question 5

What is step three of DNA replication?

Answer 5

• DNA polymerase forms phosphodiester bonds through condensation reactions, joining adjacent nucleotides on the new strand
• This forms a new DNA molecule

Question 6

Why is a DNA helix anti-parallel?

Answer 6

• DNA polymerase can only bind to the 3’ of the new template so DNA is made in opposing directions

Question 7

Who proved the semi-conservative theory?

Answer 7

Stahl and Meselson

Question 8

Explain the steps of Stahl and Meselson’s research.

Answer 8

1. They grew bacterial DNA in a sample of heavy nitrogen and light nitrogen, the replicated DNA absorbed the nitrogen as part of the nitrogenous base
2. They then centrifuged the DNA and saw the heavier DNA settled at the bottom and the lighter DNA was near the top
3. They then grew the bacteria which was in the heavier nitrogen in a sample of lighter nitrogen
4. After centrifuging, they found that the DNA was in the middle of the test tube between the heavy and light nitrogen
5. This shows that DNA replication is semi-conservative and a template strand of heavy nitrogen and a new strand of light nitrogen was used