THE MOLECULAR BASIS OF INHERITANCE
DNA REPLICATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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15N
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14N
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CsCl
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Detailed explanation-1: -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-2: -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.
Detailed explanation-3: -Scientists used Nitrogen because it gets easily incorporated into a newly synthesised DNA. Nitrogen is a major constituent of DNA. 14N is by far the most abundant isotope of nitrogen, but DNA with the heavier (but non-radioactive) 15N isotope is also functional.
Detailed explanation-4: -Meselson and Stahl use 14N and 15N isotopes in the sources of nitrogen present in the culture medium in their experiment as nitrogen is a major constituent of DNA. Moreover 15N is by far the most abundant isotope of nitrogen and DNA with the heavier 15N isotope is also functional.