Meselson-Stahl experiment Flashcards
what is semi conservative replication?
new copies of the parent DNA helix consist of half of the parent DNA - ‘half the same’
what was used to make a difference between the daughter and parent strand?
a different nitrogen isotope
what microorganism was chosen for the culture of the bacteria?
E. coli
how does N14 and N15 differ?
N14 is considered to be more ‘light’ and N15 to be more ‘heavy’
which nitrogen isotope is denser?
N15
when centrifuged in caesium chloride, what happens to the DNA?
it settles out in bands in the tube
where will the denser DNA settle?
further down the tube
what was generation 0?
all DNA was labelled with high density (15N). when centrifuged in the caesium chloride, a band of DNA settled at the bottom of the tube
what did the culture medium contain?
15 NHCl
how many generations was the E.Coli grew for?
was grown in the culture medium for 14 generations
what was generation 1?
all intermediate DNA; E.Coli with 15N DNA were transferred to a 14N medium, therefore the new strand would have to consist of the lighter 14N nucleotides.
how many times could generation 1 divide?
only once
what was generation 3?
consisted of light DNA and intermediate DNA in the ratio 3:1
with an increase in generation, what happened to the band size, and why?
the low density band size in the tube increased. this was because the only DNA available for new strand synthesis was 14N DNA
what was generation 4?
consisted of light DNA and intermediate DNA in the ratio 7:1
