Which of the following nitrogenous bases is a purine?

• A. Cytosine
• B. Uracil
• C. Thymine
• D. Guanine

Answer: (D)

Verified step by step guidance

1. Understand the structure of nucleic acids: Nucleic acids are composed of nucleotides, which include a sugar, a phosphate group, and a nitrogenous base.
2. Differentiate between purines and pyrimidines: Nitrogenous bases are categorized into two types: purines and pyrimidines. Purines have a two-ring structure, while pyrimidines have a single-ring structure.
3. Identify the purine bases: In nucleic acids, the purine bases are adenine (A) and guanine (G).
4. Identify the pyrimidine bases: The pyrimidine bases include cytosine (C), thymine (T), and uracil (U).
5. Match the given options with the purine bases: From the options provided (cytosine, uracil, thymine), none are purines. The correct purine base, as stated, is guanine.