Question

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide as only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work?

• A. There is no radioactive isotope of nitrogen.
• B. Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long.
• C. Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive.
• D. Amino acids (and thus proteins) also have nitrogen atoms. Thus, the radioactivity would not distinguish between DNA and proteins.

Answer 1

Answer: (D)

Amino acids (and thus proteins) also have nitrogen atoms. Thus, the radioactivity would not distinguish between DNA and proteins.

Alfred Hershey and Martha Chase conducted an experiment. In this Hershey and Chase experiment, they used the sulfur labeled proteins and phosphorous labeled DNA of the phage. These phages were then allowed to infect bacteria. It was observed that the DNA entered the bacterial cells and was therefore concluded to be the genetic material. The progeny of the phages that were labeled with radioactive phosphorus remained labeled whereas the progeny of the phages labeled with radioactive sulfur were unlabeled. This confirmed that DNA and not protein is the genetic material. When students used radioactive nitrogen instead of radioactive phosphorous, they did not get the required results because nitrogen is present in proteins as well as in DNA as nitrogen bases. Thus, the radioactivity did not distinguished between DNA and proteins.

Thus, the correct answer is 'Amino acids (and thus proteins) also have nitrogen atoms. Thus, the radioactivity would not distinguish between DNA and proteins.'