Final answer:
A nucleotide comprises three parts: a nitrogenous base, a pentose sugar, and a phosphate group. The base can be either purines or pyrimidines; the sugar is either ribose in RNA or deoxyribose in DNA; and the nucleotides are linked by phosphate groups.
Step-by-step explanation:
A nucleotide consists of three components: a nitrogenous base, a pentose sugar, and one or more phosphate groups. The nitrogenous base is an aromatic compound that contains nitrogen, and it can be categorized into purines, with a double ring structure; and pyrimidines, with a single ring.
Purines include adenine (A) and guanine (G), while pyrimidines include cytosine (C), thymine (T), and uracil (U) - the latter being exclusive to RNA.
The pentose sugar is a five-carbon sugar, which can be either ribose in RNA or deoxyribose in DNA, the difference being the presence of one less oxygen atom in the deoxyribose sugar of DNA.
Finally, the phosphate group is a phosphoric acid anion, which connects to the 5' carbon of the sugar and links nucleotides together to form the backbone of the DNA or RNA polymer through phosphodiester bonds.