Question

In an experiment, {E. coli is grown in a medium containing \({}^{14}NH_4Cl\) (\({}^{14}N\) is the light isotope of Nitrogen) followed by growing it for six generations in a medium having the heavy isotope of nitrogen (\({}^{15}N\)). After six generations, their DNA was extracted and subjected to CsCl density gradient centrifugation. Identify the correct density (Light/Hybrid/Heavy) and ratio of the bands of DNA in CsCl density gradient centrifugation:}

• A. Hybrid : Heavy, 1 : 16
• B. Light : Heavy, 1 : 31
• C. Hybrid : Heavy, 1 : 31
• D. Light : Heavy, 1 : 05

Hint:

DNA density gradients provide insights into replication patterns.

Answer 1

The Correct Option is C

After six generations in a \({}^{15}N\) medium, the majority of DNA will incorporate \({}^{15}N\), leading to heavy DNA. Following centrifugation, the ratio of hybrid to heavy DNA will be 1:31. This is consistent with the result after six generations in a \({}^{15}N\) medium, where most DNA becomes heavy, yielding a hybrid to heavy DNA ratio of 1:31 post-centrifugation.