Semiconservative mechanism of DNA was detected using:

Options

A. `""^(35)S`
B. `""^(14)C`
C. `""^(32)P`
D. `""^(15)N`

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the detection of the semiconservative mechanism of DNA replication. This mechanism suggests that during DNA replication, each new DNA molecule consists of one old (parental) strand and one newly synthesized strand.

2. **Identifying the Scientists**: The experiment that demonstrated the semiconservative nature of DNA replication was conducted by scientists Matthew Meselson and Franklin Stahl in 1958.

3. **The Experiment Setup**: Meselson and Stahl used two isotopes of nitrogen for their experiment: Nitrogen-15 (N-15) and Nitrogen-14 (N-14). They chose these isotopes because nitrogen is a key component of DNA.

4. **Labeling the DNA**: They grew E. coli bacteria in a medium containing N-15, which made the DNA of these bacteria heavy. After several generations, the bacteria were then transferred to a medium containing N-14, allowing them to replicate their DNA in the presence of the lighter isotope.

5. **Analyzing the Results**: After one round of replication in the N-14 medium, the DNA was extracted and analyzed using density gradient centrifugation. The results showed that the DNA consisted of hybrid molecules, each containing one strand of N-15 and one strand of N-14.

6. **Conclusion**: The presence of hybrid DNA confirmed that the replication of DNA is semiconservative, as each new DNA molecule consisted of one original strand and one new strand. Thus, the semiconservative mechanism of DNA replication was detected using the isotopes of nitrogen, specifically N-15.

**Final Answer**: The semiconservative mechanism of DNA was detected using Nitrogen-15 (N-15).

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