Complete the comparison of the metabolic pathways leading to thymine in DNA and thymine as a modified base in tRNA. Thymine in DNA occurs as the result of thymidylate synthase creating , which then undergoes to , then to , and incorporated into DNA by .

The question is incomplete, the complete question is as follow:

Thymine in DNA occurs as the result of thymidylate synthase creating , which then undergoes to , then to , and incorporated into D N A by . Thymine in tRNA arises , by an S-adenosylmethionine-dependent of a residue in RNA.

Thymine in DNA occurs as the result of thymidylate synthase creating dTMP, which then undergoes phosphorylation to dTDP, then to dTTP, and incorporated into DNA by DNA polymerase. Thymine in tRNA arises posttranslationally, by an S-adenosylmethionine-dependent methylation of a UMP residue in RNA.

Explanation:

Thymidylate synthase is a key enzyme that catalyzes the synthesis of 2′-deoxythymidine-5′-monophosphate (dTMP) from 2′-deoxyuridine-5′-monophosphate (dUMP). This enzyme catalyzes the addition of a phosphate group (phosphorylation) of dTMP in order to form thymidine 5'-diphosphate (dTDP). Once synthesized, dTMP can be metabolized to deoxythymidine triphosphate (dTTP), which is a precursor for DNA biosynthesis. On the other hand, transfer ribonucleic acid (tRNA) is methylated after the molecule is synthesized. The transfer of the methyl group is catalyzed by an S-adenosylmethionine–dependent methyltransferase that catalyzes the methylation of uridine monophosphate (UMP) using SAM (S-adenosylmethionine) as the methyl donor.