Question

Purines found both in DNA and RNA are
A. Adenine and thymine
B. Adenine and guanine
C. Guanine and cytosine
D. Cytosine and thymine

Answer 1

Hint:
Purine is a large sized heterocyclic aromatic organic compound that consists of two rings in their structure. It contains four nitrogen atoms at 1, 4, 3, 7 and 9 positions. It is water-soluble. Purines (adenine and guanine) are found both in DNA and RNA.

Complete answer:
Nucleic acids are composed of 3 components namely nitrogenous bases, pentose (5 carbon) sugars and one or more phosphate groups. Purines and pyrimidines are the two main kinds of nitrogenous bases that make up nucleic acids. In other words, they are the building blocks of DNA and RNA. Purine is a heterocyclic aromatic organic compound that consists of two rings in their structure. It is a nine membered double ring with four nitrogen atoms at 1, 4, 3, 7 and 9 positions. There are two main types of purine known as Adenine and Guanine. Both of these purines occur in both DNA and RNA. Pyrimidines are smaller sized simple aromatic compounds that are composed of carbon and nitrogen atoms in a six-membered ring. It is a single ring with nitrogen at 1 and 3 positions. There are three main types of pyrimidines, Cytosine, uracil and thymine. However only one of these pyrimidines exists in both DNA and RNA: Cytosine. The other two are Uracil, which is RNA exclusive, and Thymine, which is DNA exclusive. While they are similar in many aspects, there are so many key differences between them.

So, the correct answer is option B.

Note: Adenine and guanine are purines while cytosine, thymine and uracil are pyrimidines. In both the DNA and RNA purine are same while among pyrimidines, thymine is present in DNA and uracil in RNA.