Question

A certain bacterium was cultured for several generations in medium containing 15N, transferred to medium containing 14N, and allowed to complete two rounds of cell division. Given that the bacterium’s genome mass is 5.4 fg when grown in 14N media and 5.5 fg when grown in 15N medium, individual bacteria with which of the following genome masses would most likely be isolated from this culture? A.5.4 fg only B.5.4 fg and 5.45 fg C.5.4 fg and 5.5 fg D.5.45 fg only

Answer 1

Answer:

The correct answer is option B.

Explanation:

On seeing the question, it is clear that it is based upon the concept of semi-conservative theory for the replication of DNA. It is mentioned that when the bacteria were grown on N-15, the mass was 55 fg. Now, after two generations, the DNA would comprise N-14 and the mass of them will be 5.4 fg.  

The average mass would be = 5.4 + 5.5 / 2 = 10.9 / 2 = 5.45 fg. The mass of the bacteria isolated from the culture would possibly contain both the masses. That is, the mass of DNA with N-14 only would be 5.4 fg, and the mass of DNA with both N-15 and N-14 would be the average, that is, 5.45 fg.