What are the two main types of nitrogenous bases in nucleic acids?

• A. Purines and pyrimidines
• B. Amino acids and nucleotides
• C. Ribose and deoxyribose
• D. DNA and RNA

Answer: (A)

Nitrogenous bases in nucleic acids are categorized mainly into two types: purines and pyrimidines. Purines, which include adenine and guanine, are characterized by a double-ring structure. Pyrimidines, on the other hand, consist of a single-ring structure and include cytosine, thymine (found in DNA), and uracil (found in RNA). This distinction is crucial because the type of nitrogenous base influences the structure and function of nucleic acids, such as DNA and RNA.

The other options do not correctly identify the main types of nitrogenous bases. Amino acids and nucleotides are components of proteins and nucleic acids respectively, but they refer to different classes of biomolecules. Ribose and deoxyribose are sugars found in RNA and DNA, while DNA and RNA themselves refer to whole nucleic acids, not specific types of nitrogenous bases. Hence, identifying purines and pyrimidines as the two main types helps in understanding the fundamental composition of nucleic acids.