Final answer:
The class of molecules known as nucleotides is best described as a combination of a nitrogenous base, a phosphate group, and a pentose sugar. These three components form the essential building blocks of DNA and RNA, with nucleotides being the subunits of these vital cellular components.
Step-by-step explanation:
The description that best fits the class of molecules known as nucleotides is: a nitrogenous base, a phosphate group, and a pentose sugar. Nucleotides are the building blocks of nucleic acids like DNA and RNA. Each nucleotide is comprised of three main components:
- A nitrogen-containing base: These include purines (adenine and guanine) with a double ring structure and pyrimidines (cytosine, thymine, and uracil) with a single ring.
- A pentose sugar: This can either be deoxyribose, found in DNA, or ribose, found in RNA. The difference between these sugars is the presence of an OH group on the 2' carbon in ribose, while deoxyribose has an H at the same position.
- One or more phosphate groups: Phosphate groups are attached to the 5' carbon of the sugar and are key to the nucleotide's ability to form the backbone of nucleic acid chains.
The fusion of these three components makes nucleotides versatile molecules that can be assembled into the long chains of DNA or RNA, or serve in energy transfer as in the molecule adenosine triphosphate (ATP).