3.1.5.2 DNA Replication

Question 1

Why does DNA replicate before mitosis and meiosis?

Answer 1

DNA replicates itself to ensure that daughter cells have all the genetic information to produce enzymes and proteins.

Question 2

What does semi-conservative replication mean?

Answer 2

Molecule will contain an original strand a new strand.

Question 3

Why is semi-conservative replication important?

Answer 3

Ensures genetic continuity

Question 4

Outline the steps of semi-conservative replication

Answer 4

1) DNA helicase breaks hydrogen bonds between bases on two strands of DNA causing the helix to unwind.
2) Original strands act as templates for new strands, free floating DNA nucleotides are attracted to their complementary bases on each original strand.
3) DNA polymerase catalyses condensation reactions which join the nucleotides of the new strands together by phosphodiester bonds causing hydrogen bonds to form between the bases between original and new strands.

Question 5

Which scientists determined semi-conservative replication?

Answer 5

Meselsen and Stahl

Question 6

How did scientists prove semi-conservative replication?

Answer 6

1) Bacteria grown on heavy 15N nitrogen forming heavier DNA.
2) Placed in lighter 14N nitrogen conditions causing an intermediate density because of 15N and 14N.
3) Replicated in 14 N again so lighter and intermediate density DNA are incorporated.