2.2 DNA replication

Question 7

Describe the process of semi-conseravtive DNA replication. (7)

Answer 7

• DNA helicase breaks the hydrogen bonds between the two DNA strands and the DNA helix unwinds
• Each strand acts as a template for a new strand
• Individual free DNA nucleotides join up along the template strand by complementary base pairings
• DNA polymerase joins the individual nucleotides together, so that the sugar-phosphate backbone forms
• Hydrogen bonds them form between the bases on each strand and the strand twist to form a double-helix
• Two identical DNA molecules are produced
• Each of the new molecules contains a single strand from the original DNA molecule and a single new strand

Question 8

Who discovered the structure of DNA

Answer 8

Watson and Crick
They hypothesied that DNA must replicate either conservatively or semi conservatively

Along with the help of Rosalind Franklin

Question 9

What was their first hypothesis

Answer 9

That DNA was replicated semi conservatively-Each replicated DNA molecule contains one of the original DNA strands strand and one newly synthesied DNA strand

Question 10

What was the second hypothesis

Answer 10

That DNA was replicated conservatively-The original DNA remains intact following DNA replication and the two newly synthesised strands of DNA join together

Question 11

What are the three experimental background information

Answer 11

1. DNA bases are nitrogenous
2. Nitrogen has two isotopes N14 and N15
3. Bacteria take in the nitrogen isotopes to make new DNA nucelotides

Question 12

How would you determine which DNA sample has Isotope N15 or N14

Answer 12

Spin the sample in a centrifuge to determine thier density
N15 will settle lower down as it is more dense
N14 will settle high as it is more less dense