Question

A radioisotope of which element would effectively label phage protein but not DNA?

a)Phosphorus
b)Nitrogen
c)Carbon
d)Sulfur
e)Oxygen

Answer 1

To label phage protein without labeling DNA, radioactive sulfur (35S) is used because it is present in proteins but absent in DNA. Therefore, the correct element for such labeling would be sulfur.

Step-by-step explanation:

Radioisotope Labeling in Bacteriophages

To selectively label the protein coat of a phage without labeling its DNA, a radioisotope of an element found in proteins but not in nucleic acids should be used. In the landmark Hershey and Chase experiments, the choice was to use radioactive sulfur (35S) because sulfur is a component of the amino acids methionine and cysteine, which are present in proteins, but it is not found in DNA. On the other hand, radioactive phosphorus (32P) was used to label DNA due to the presence of phosphorus in the backbone of DNA molecules. Consequently, the correct answer for a radioisotope that would label phage protein but not DNA is (d) Sulfur.