DNA replication Flashcards
What is the 1st stage of DNA replication?
2 strands of DNA separates - uses DNA helices
What is the 2nd stage of DNA replication after the strands separate?
Free DNA nucleotides pair with complimentary bases (Hydrogen bonds form)
What is the 3rd stage of DNA replication after the DNA nucleotides pair with the complimentary bases?
New DNA nucleotides bond together - phosphodiester bonds, condensation reaction, joined by DNA polymerase
Now 2 identical strands of DNA
Are both of the strands of DNA used as templates in replication?
Yes
What is DNA replication known as and why?
Semi-conservative as each new molecule contains one of the original strands
How did scientists also suggest that DNA replication could occur?
Conservative replication - one daughter molecule is made of entirely new material, the other is made of the original material
What are the scientists that found the evidence for semi-conservative replication called?
Meselson and Stahl - they designed an experiment to determine the mechanism of DNA replication
What do all DNA bases contain?
Nitrogen
What are the 2 forms of nitrogen?
N14 - less dense
N15 - more dense
What will bacteria do with nitrogen growing in their medium?
Incorporate it into any new DNA they make
What was the experiment that meselson and stahl carried out to determine the mechanism of DNA replication?
They grew E.coli on a medium containing the heavy isotope N15 for many generations, so ‘all’ the DNA was labelled with heavy N
What was the E.coli medium transferred to in the meselson and stahl experiment?
The bacteria was transferred to a medium containing the lighter isotope of nitrogen N14 for 1, 2 or 3 generations
What is the evidence that DNA replicates semi-conservatively?
In meselson and stahl’s experiment, after the new bacteria was centrifuged, there was one line formed - N14 and N15 DNA
In meselson and stahl’s experiment, what would of happened if conservative replication occurred?
2 lines would have been formed - one N15 and one N14
