AP BIOLOGY

THE MOLECULAR BASIS OF INHERITANCE

DNA REPLICATION

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Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]

Is 14N’s density heavier, lighter, or equal compared to 15N?

A	heavier
B	lighter
C	equal to

Explanation:

Detailed explanation-1: -Under these circumstances, the DNA will form a band according to its density in the gradient. DNA grown in 15N will band at a higher density position than that grown in 14N.

Detailed explanation-2: -The semi-conservative nature of DNA replication was established by Meselson and Stahl in their classic experiment with bacteria They grew bacteria in N15−NH4Cl containing medium, washed and then incubated in fresh medium with N14-containing compounds and allowed to grow for three generations.

Detailed explanation-3: -coli fully labelled with N15N15 is allowed to grow in N14N14 medium, then after fist genertion of replication one of the two strands would have N15 and the other strand would have N14. The two strands of DNA molecule of the first generation bacteria have different density and resemble parent DNA.

Detailed explanation-4: -coli cells with 15N-dsDNA are incubated in medium containing 14N nucleotide. After 60 minutes, 60 E. coli cells will have DNA totally free from 15N.

There is 1 question to complete.