Question

To prove that $DNA$ is the genetic material, which radioactive isotopes were used by Hershey and Chase $(1952)$ in their experiments?

• A. ${}^{35}S$ and ${}^{15}N$
• B. ${}^{32}P$ and ${}^{35}S$
• C. ${}^{32}P$ and ${}^{15}N$
• D. ${}^{14}N$ and ${}^{15}N$

Answer 1

Answer: (B)

Hershey and Chase experiment is based on the fact that $DNA$ contains phosphorus and similarly sulphur is present in proteins but not in $DNA$. They incorporated radioactive isotope of phosphorus (${}^{32}P$) into phage $DNA$ and that of sulphur (${}^{35}S)$ into proteins of a separate phage culture. Viruses grown in the presence of radioactive phosphorus contained radioactive $DNA$ but not radioactive protein because $DNA$ contains phosphorus but proteins do not. Similarly, viruses grown on radioactive sulphur contain radioactive protein but not radioactive $DNA$ because $DNA$ does not contain sulphur.