Nucleotides are composed of which components and what are the roles of the polymerases?

• A. Nucleotides are fats, sugars, and acids.
• B. Nucleotides are sugar, phosphate, and base; DNA polymerase builds DNA during replication; RNA polymerase synthesizes RNA during transcription.
• C. Nucleotides are amino acids; DNA polymerase repairs proteins; RNA polymerase degrades RNA.
• D. Nucleotides are sugar, phosphate, and base; DNA polymerase synthesizes RNA; RNA polymerase synthesizes DNA.

Answer: (B)

Nucleotides are the basic units of nucleic acids, made of a sugar, a phosphate group, and a nitrogenous base (with deoxyribose in DNA and ribose in RNA). DNA polymerase builds DNA during replication by adding complementary nucleotides to a growing strand, using the existing strand as a template. RNA polymerase carries out transcription, reading the DNA template and producing an RNA molecule. The other options misstate the composition or assign incorrect roles to the enzymes—for example, nucleotides aren’t fats or amino acids, and polymerases don’t swap functions like synthesizing RNA when DNA is the template and vice versa.