Questions: Which is incorrect about purines? a. only found in DNA, not in RNA b. are nitrogenous bases c. always paired with a specific pyrimidine d. include adenine and guanine e. found within nucleotides

The answer is the first one (a): only found in DNA, not in RNA.

Explanation for each option:

a. Only found in DNA, not in RNA - This statement is incorrect. Purines, specifically adenine and guanine, are found in both DNA and RNA. Therefore, this option is incorrect.

b. Are nitrogenous bases - This statement is correct. Purines are a type of nitrogenous base, which are essential components of nucleic acids.

c. Always paired with a specific pyrimidine - This statement is correct. In DNA, adenine (a purine) pairs with thymine (a pyrimidine), and guanine (a purine) pairs with cytosine (a pyrimidine). In RNA, adenine pairs with uracil (a pyrimidine).

d. Include adenine and guanine - This statement is correct. Adenine and guanine are the two purines found in nucleic acids.

e. Found within nucleotides - This statement is correct. Purines are part of nucleotides, which are the building blocks of nucleic acids like DNA and RNA.

In summary, the incorrect statement about purines is that they are only found in DNA, not in RNA.