Meselson-Stahl experiment Flashcards

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1
Q

what is semi conservative replication?

A

new copies of the parent DNA helix consist of half of the parent DNA - ‘half the same’

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2
Q

what was used to make a difference between the daughter and parent strand?

A

a different nitrogen isotope

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3
Q

what microorganism was chosen for the culture of the bacteria?

A

E. coli

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4
Q

how does N14 and N15 differ?

A

N14 is considered to be more ‘light’ and N15 to be more ‘heavy’

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5
Q

which nitrogen isotope is denser?

A

N15

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6
Q

when centrifuged in caesium chloride, what happens to the DNA?

A

it settles out in bands in the tube

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7
Q

where will the denser DNA settle?

A

further down the tube

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8
Q

what was generation 0?

A

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

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9
Q

what did the culture medium contain?

A

15 NHCl

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10
Q

how many generations was the E.Coli grew for?

A

was grown in the culture medium for 14 generations

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11
Q

what was generation 1?

A

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.

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12
Q

how many times could generation 1 divide?

A

only once

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13
Q

what was generation 3?

A

consisted of light DNA and intermediate DNA in the ratio 3:1

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14
Q

with an increase in generation, what happened to the band size, and why?

A

the low density band size in the tube increased. this was because the only DNA available for new strand synthesis was 14N DNA

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15
Q

what was generation 4?

A

consisted of light DNA and intermediate DNA in the ratio 7:1

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