Which of the following is a purine base of nucleic acids?

Adenine

The correct answer is option 1. Adenine. 

Let us delve into the details of purine and pyrimidine bases, focusing on their structures and roles in nucleic acids.

Bases of Nucleic Acids

Nucleic acids, such as DNA and RNA, are made up of nucleotides, each of which contains a nitrogenous base, a sugar, and a phosphate group. The nitrogenous bases are classified into two categories: purines and pyrimidines.

Purines

Purines have a double-ring structure composed of a six-membered and a five-membered ring fused together. The two purine bases found in nucleic acids are:

Adenine (A):

Adenine has a fused double-ring structure with 9 atoms (6 carbons and 3 nitrogens).

In DNA, adenine pairs with thymine, and in RNA, it pairs with uracil. Adenine is crucial for the genetic code and energy transfer (e.g., ATP).

Guanine (G):

Guanine also has a double-ring structure, similar to adenine, but with additional oxygen and nitrogen atoms.

In both DNA and RNA, guanine pairs with cytosine. It plays an essential role in the structure and function of nucleic acids.

Pyrimidines

Pyrimidines have a single-ring structure with six members. The three pyrimidine bases found in nucleic acids are:

Cytosine (C):

Cytosine has a single-ring structure with an amine group and a carbonyl group.

In DNA and RNA, cytosine pairs with guanine. It is involved in encoding genetic information.

Thymine (T):

Thymine has a single-ring structure with a methyl group and two carbonyl groups.

Thymine is found only in DNA, where it pairs with adenine.

Uracil (U):

Uracil has a similar structure to thymine but lacks the methyl group.

Uracil is found only in RNA, where it pairs with adenine.

Summary of Nitrogenous Bases

Purine Bases: Adenine (A) and Guanine (G)

Pyrimidine Bases: Cytosine (C), Thymine (T) (in DNA), and Uracil (U) (in RNA)

In Summary:

Adenine is a purine base, characterized by its double-ring structure. Uracil, Thymine, and Cytosine are pyrimidine bases, characterized by their single-ring structures. Therefore, among the options provided, Adenine is the purine base of nucleic acids.