Question

Among the nitrogenous bases involved in DNA and RNA formation, which is the double-ring base?
A. Uracil
B. Guanine
C. Thymine
D. Cytosine

Answer 1

Hint: The term DNA stands for deoxyribonucleic acid and RNA stands for ribonucleic acid. DNA and RNA are both nucleic acids and either of them is present in the nucleus of the cell. It is the genetic material of an organism. Purines have double-ringed structures.

Complete answer: The structure of DNA is coiled helical in shape which consists of two polynucleotide chains. DNA carries the genetic instruction for the functioning, development, reproduction, and growth of all known organisms and also many viruses. Therefore, DNA is considered as the genetic material of an organism. Polynucleotides consist of smaller monomeric units called nucleotides. Each nucleotide is made up of three components: a deoxyribose sugar, a nitrogen-containing nucleobase, and a phosphate group. The main difference between DNA and RNA is the sugar component and the nitrogenous base. In RNA, the sugar called ribose is present instead of deoxyribose and nitrogenous base uracil is present instead of thymine. The sugar of one nucleotide is attached to the phosphate group of another nucleotide by a covalent bond. An organic molecule that contains a nitrogen atom which has chemical properties like the base is called the nitrogenous base. The five types of nitrogenous base are adenine, guanine, uracil, thymine, and cytosine. From the above-mentioned options, guanine is a derivative of purines and has a double ring structure. Guanine is paired with cytosine in DNA. The chemical formula of guanine is C5H5N5O.
So, option B is the correct answer.

Note: Pyrimidines and purines are two-parent compounds from which the nitrogenous bases are derived. Thymine, cytosine, and uracil are included in pyrimidines and have a single ring structure. These nitrogenous bases in DNA are bonded together by hydrogen bonds. Adenine pairs with thymine by double hydrogen bonds, while guanine pairs with cytosine by triple hydrogen bonds.