Question

If 14C-labeled uracil is added to the growth medium of cells, what macromolecules will be labeled?

DNA
RNA
both DNA and RNA
polypeptides

Answer 1

When 14C-labeled uracil is added to the growth medium of cells, it will primarily be incorporated into RNA. Uracil is one of the four nucleotide bases that make up RNA (the others being adenine, cytosine, and guanine). In the synthesis of RNA, uracil replaces thymine, which is found in DNA.

However, uracil is not used in the synthesis of DNA; instead, thymidine is used as the corresponding nucleotide base in DNA. Therefore, if 14C-labeled uracil is incorporated into cellular molecules, it will specifically label RNA.

The correct answer is: **RNA**.