Question

a. Would you expect virus growing in a medium containing 35S to synthesize DNA containing 35S?

A.No

B.Yes

C.Yes, but only a little

b. Which statement best reflects your reasoning?

A.DNA is made up of sugar, phosphate, and nitrogenous bases. None of these molecules contain sulfur, so 35S wouldn’t become part of the DNA.

B.I think DNA might contain sulfur, so 35S could become part of DNA made by virus in a 35S solution.

C.35S sticks to any biomolecule, so newly synthesized DNA would be contaminated with 35S.

Answer 1

a. I wouldn't expect virus growing in a medium containing 35S to synthesise DNA containing 35S. So, the correct option is A.

b. The correct option is A. When radioactive sulphur atoms are present, they are incorporated into the protein coats and not in the DNA since two of the amino acids cysteine and methionine contain sulphur. On the other hand, DNA is made up of pentose sugar, N₂ bases and phosphate which do not contain sulphur. So, sulphur won't become part of the DNA.