Semi-conservative DNA replication 2.1.3e

Question 1

Describe the process of semi-conservative DNA replication

Answer 1

1) DNA helicase causes the 2 polynucleotide strands to unzip - as it breaks the hydrogen bonds
2) Each original strand acts as a template - attracting free complimentary bases
3) Nucleotides and bases joined together by DNA polymerase (hydrogen bonds), forming sugar-phosphate backbone.
4) 2 identical strands are formed
- All nucleotides are joined to form a complete polynucleotide
- Each strand retains half the original DNA ‘semi-conservative’

Question 2

What is the function of DNA helicase?

Answer 2

Breaks hydrogen bonds between bases, unzipping the DNA strands

Question 3

What is the function of DNA polymerase?

Answer 3

Joins free nucleotides to the original strand

Question 4

What is the evidence for semi-conservative DNA replication?

Answer 4

Meselsohn and Stahl - E.coli
Parental generation - both strands made with 15N
First generation - DNA made of one strand 15N and one strand 14N
Second generation - some DNA made of 2 strands of 14N and some made of 15N and 14N.