Which of the following statements is true about purines?

Purines are a class of nitrogenous bases that are essential components of nucleotides, which are the building blocks of DNA and RNA. The correct statement asserts that purines include adenine and guanine. Both of these nucleobases have a double-ring structure made up of carbon and nitrogen atoms, distinguishing them from pyrimidines, which have a single-ring structure.

Adenine and guanine play critical roles in a variety of biochemical processes, including the synthesis of nucleic acids. In DNA, adenine pairs with thymine, and in RNA, it pairs with uracil. Guanine pairs with cytosine in both DNA and RNA. The presence of purines in the structure of nucleic acids is fundamental to the storage and transmission of genetic information.

Other statements do not accurately reflect the properties of purines. For instance, purines do not consist of a single carbon-nitrogen ring; that describes pyrimidines. Additionally, purines are not shorter than pyrimidines; they are actually larger due to their double-ring structure. Lastly, purines are indeed found in DNA, as both adenine and guanine are integral components of the DNA molecule.