Which nucleotide listed is involved in DNA?

In DNA, the nucleotides that are incorporated include specific bases that pair to form the double helix structure. Thymidine, which is the correct answer, is a nucleoside derived from thymine, one of the four bases in DNA. In the context of DNA, thymine specifically pairs with adenine through two hydrogen bonds, forming essential connections in the double-stranded structure of DNA.

The other options do not serve as components of DNA. Uridine, for instance, is associated with RNA—where uracil replaces thymine as one of the four bases. Adenosine is a nucleoside as well but is not exclusively tied to DNA; it is found in both DNA and RNA processes but relates to energy transfer and signaling rather than basic nucleotide pairing in DNA. Guanosine, like adenosine, is involved in both RNA and DNA but primarily represents guanine in those contexts.

Thus, thymidine is the optimal choice when identifying a nucleotide specifically related to the structure and function of DNA within the broader molecular biology framework.