How did Hershey and Chase use radioactivity to determine whether proteins or $\mathrm{DNA}$ were the genetic material?

• A. They labeled $\mathrm{DNA}$ with radioactive sulfur and proteins with radioactive phosphorus.
• B. They labeled both $\mathrm{DNA}$ and proteins with radioactive carbon.
• C. They used radioactive nitrogen to label both $\mathrm{DNA}$ and proteins.
• D. They labeled proteins with radioactive sulfur and $\mathrm{DNA}$ with radioactive phosphorus.

Answer: (D)

Verified step by step guidance

1. Understand the context: Hershey and Chase conducted experiments to determine whether DNA or proteins were the genetic material in cells.
2. Identify the key components: Proteins contain sulfur, while DNA contains phosphorus. This distinction is crucial for labeling.
3. Labeling strategy: Hershey and Chase used radioactive isotopes to label the components. They labeled proteins with radioactive sulfur (\(^{35}\text{S}\)) because sulfur is present in proteins but not in DNA.
4. Labeling DNA: They labeled DNA with radioactive phosphorus (\(^{32}\text{P}\)) because phosphorus is present in DNA but not in proteins.
5. Analyze the results: After allowing the bacteriophages to infect bacteria, they observed which radioactive label entered the bacterial cells, concluding that DNA was the genetic material because the radioactive phosphorus was found inside the cells.