DNA replication
- Created by: jessicawarren
- Created on: 17-03-16 13:08
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- DNA Replication
- Semi Conservative Replication
- 1: DNA helicase breaks hydrogen bonds between bases on polynucleotide strands. Helix unwinds to form two single strands.
- 2: Each original strand acts as template for new strand. Complementary base pairing means free floating DNA nucleotides attracted to exposed bases
- 3: Condensation reactions join nucleotides of new strands together catalysed by DNA polymerase. Hydrogen bonds form between bases on original and new strands
- 4: Each new DNA molecule contains one strand from original DNA and one new strand
- DNA Polymerase
- Active site complementary to 3' end of DNA
- Can only add nucleotides to 3' end
- Moves in opposite ways along anti parallel DNA strands
- Evidence for SCR
- Meselson and Stahl
- Two nitrogen isotopes: heavier 15N and iighter 14N
- SCR Practical
- Two samples of bact. grown- one light, one heavy nitrogen. As bact. reproduce, take up nitrogen
- Sample of DNA taken from each batch, spun in centrifuge. DNA from heavy N settles lower in tube than light N.
- Bact from heavy N taken out and put in broth containing light N. Bact left to replicate
- New bact DNA molecules contain one strand of old DNA (heavy N) and one strand of new (light N)
- Semi Conservative Replication
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