DNA replication Flashcards
1) Describe the process of DNA replication (typical 4/5 marker)
Dna helicase travels down the DNA, breaking the H bonds between bases forming two individual strands. Free dna nucleotides in the nucleus form H bonds via complimentary base pairing with the strands. DNA Polymerase runs along the dna nucleotides forming phosphodiester bonds between nucleotides forming sugar phosphate backbone.
2) Explain how Meselson and Stahl’s experiment provides evidence for the semi-conservative model of DNA replication
-used heavy and light dna strands with heavier and lighter isotopes of nitrogen
-moved 15N into a medium containing only normal 14N
-allowed the bacteria to divide and their DNA to replicate once
-they extracted and centrifuged the DNA (heavy DNA should sink to the bottom and light DNA should rise to the top)
-their result was a single band of medium density DNA meaning the new DNA molecules contained one parent strand and one new strand-one heavy and one light
3) Explain how Meselson and Stahl’s experiment refuted the conservative model of DNA replication
If the conservative model was correct the DNA molecules after one division would either have 2 original parent strands or 2 new strands and the DNA molecules with new strands would rise to the top and the DNA with the parent strands would sink to the bottom, since the DNA strands formed a single band of medium density DNA the replicated DNA couldnt have fully conserved their origional nucleotides as that wouldve made some strands heavier and some lighter so they wouldnt lf formed a single band
4) Explain how Meselson and Stahl’s experiment refuted the dispersive model of DNA replication
if the dispersive model was correct then there would be random combinations of heavier and lighter DNA molecules in the mew strands so the strands would end up at many different height of the tube
