An E.coli with heavy DNA molecule is transferred into the medium with normal nitrogen (N 14H4Cl ). After 40 minutes what will be the percentage of heavy DNA molecule ?

The E.coli cell will have 15N15N strand. This is grown on a medium containing 14NH4Cl for 40 minutes which is actually 2 generations as the generation time for E.coli is 20 minutes. So after 1st 20 minutes two hybrid (15N14N) will be produced.Then these strand goes for another round of replication, then 2 hybrid DNA (15N14N) and 2 light DNA (14N14N) will be produced. So we can see that there is no formation of heavy DNA.

An E.coli with heavy DNA molecule is transferred into the medium with normal nitrogen (N 14H4Cl ). After 40 minutes what will be the percentage of heavy DNA molecule ?

The E.coli cell will have 15N15N strand. This is grown on a medium containing 14NH4Cl for 40 minutes which is actually 2 generations as the generation time for E.coli is 20 minutes. So after 1st 20 minutes two hybrid (15N14N) will be produced.Then these strand goes for another round of replication, then 2 hybrid DNA (15N14N) and 2 light DNA (14N14N) will be produced. So we can see that there is no formation of heavy DNA.

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An E.coli with heavy DNA molecule is transferred into the medium with normal nitrogen ( ${}^{14}N H_{4} C l$ ). After 40 minutes what will be the percentage of heavy DNA molecule ?

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Detailed Solution

The E.coli cell will have ¹⁵N¹⁵N strand. This is grown on a medium containing ¹⁴NH₄Cl for 40 minutes which is actually 2 generations as the generation time for E.coli is 20 minutes.

So after 1st 20 minutes two hybrid (¹⁵N¹⁴N) will be produced.

Then these strand goes for another round of replication, then 2 hybrid DNA (¹⁵N¹⁴N) and 2 light DNA (¹⁴N¹⁴N) will be produced. So we can see that there is no formation of heavy DNA.

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