DNA Replication

Question 1

DNA ( semi conservative ) replication:

Answer 1

1. DNA helicase breaks the hydrogen bonds and the two strands unwind
2. Free floating DNA nucleotides line up by complementary base paring. This happens opposite both parent strands. ( include base parings )
3. Condensation reaction catalysed by DNA polymerase joins adjacent nucleotides nucleotides via phosphodiester bonds to form 2 strands.
4. Hydrogen bonds form between the bases of the new strand and the parent strand and the helix reforms.
5. There is now an identical copy of DNA in two new cells. One strand is the original ( parent ) and the other is newly formed.

Question 2

DNA polymerase:

Answer 2

DNA polymerases active site is complementary to the 3’ end of the newly forming strand so it moves in a 5’ -> 3’ direction.
Because the two strands are antiparallel, it therefore moves in a 3’ -> 5’ direction across the original strand.

Question 3

Who determined the structure of DNA?

Answer 3

Watson and Crick.

Question 4

Who discovered evidence for semi conservative DNA replication?

Answer 4

Meselson and Stahl’s

Question 5

Meselson answered Stahl’s experiment:

Answer 5

1. Grow bacteria in N15.
2. Transfer cells to N14, grow for one direction.
3. Grow for second generation in N14.
4. Heavy DNA ( N15 ).
5. Hybrid DNA ( N15 + N14 ).
6. ‘Light’ DNA ( N14 ) + Hybrid DNA ( N15 + N14 )