Which of the following words can be used to describe the nitrogenous bases found in both DNA and RNA?
a. purine
b. pyrimidine
c. imidazole
d. both purine and pyrimidine
e. both pyrimidine and imidazole
The correct answer and explanation is:
The correct answer is d. both purine and pyrimidine.
Nitrogenous bases in both DNA and RNA can be categorized into two major classes: purines and pyrimidines. These categories refer to the chemical structure of the bases.
- Purines: This class includes adenine (A) and guanine (G). Purines are characterized by a two-ring structure. Both adenine and guanine are found in both DNA and RNA. In DNA, adenine pairs with thymine, and guanine pairs with cytosine. In RNA, adenine still pairs with uracil instead of thymine, while guanine continues to pair with cytosine.
- Pyrimidines: This class includes cytosine (C), thymine (T), and uracil (U). Pyrimidines have a single-ring structure. Thymine is found only in DNA, where it pairs with adenine. In RNA, thymine is replaced by uracil, which pairs with adenine. Cytosine is found in both DNA and RNA, where it always pairs with guanine.
Imidazole is a heterocyclic aromatic compound that forms part of the structure of purines, but it is not a direct descriptor for the nitrogenous bases in DNA or RNA. Therefore, imidazole cannot be used to describe the nitrogenous bases found in DNA and RNA.
In summary, purines and pyrimidines are the terms used to describe the nitrogenous bases in both DNA and RNA, making option d the correct choice. These two classes of bases are crucial in encoding genetic information and facilitating the processes of transcription and translation.