Question

If E.coli is allowed to grow for 40 minutes in a medium containing $N^{15}$ , then the number of $N^{14}/N^{14}$ containing DNA would be

• A. Zero
• B. 10
• C. 24
• D. 20

Answer 1

The correct option is A Zero

• The experiment performed by Messelson and Stahl proves that the replication pattern of the DNA is semi-conservative. The DNA helix is composed of two strands.
• During replication, the strands separate and the new strands are formed on the original template strands.
• One of the strand remains the older and one new strand is synthesized and the process is known as semi-conservative. Since, the cells are grown in medium containing N${}^{15}$ so there will be no strand with N${}^{14}$/ N${}^{14}$.

Thus, the correct answer is option A.