Question 10

A and N are the two bases that are purines.

Purines are a type of nitrogenous base that include adenine (A) and guanine (G). In this case, adenine (A) is explicitly mentioned as a purine, while the other choices do not include guanine but instead include bases that are not purines.

A) A

Adenine (A) is one of the two purines found in nucleic acids. It is essential for various biological functions, including its role in DNA and RNA structure.

B) C

Cytosine (C) is not a purine; it is classified as a pyrimidine. Pyrimidines, unlike purines, have a single-ring structure, whereas purines have a double-ring structure.

C) T

Thymine (T) is also a pyrimidine and not a purine. Like cytosine, it has a single-ring structure and is part of DNA but does not fall into the purine category.

D) N

The letter N does not represent any specific nitrogenous base. It is not classified as a purine or a pyrimidine and, therefore, is not relevant in this context.

Conclusion

Adenine (A) is definitively a purine, while the other options fail to meet the criteria of being purines. Cytosine (C) and thymine (T) are both pyrimidines, and the letter N does not represent a nitrogenous base at all. Thus, A is the correct choice, and no other options qualify as purines.