Question

Which one is not a constituent of nucleic acid?
A. Uracil.
B. Guanidine.
C. Phosphoric acid.
D. Ribose sugar.

Answer 1

Hint: Each and every nucleic acid is made up of four out of five possible nitrogenous bases i.e., nitrogen containing bases. These are adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). With these nitrogenous bases, phosphate groups and pentose sugar form the backbone of nucleic acids.

Complete step by step answer:
Core structure of nucleic acids is as follows-
Nucleic acids are made up of polynucleotide, that is, long chain like structure and composed of a series of almost identical building blocks called as nucleotides.
Each and every nucleotide consists of a nitrogen-containing aromatic base that is attached to a five carbon sugar called pentose sugar, which is further attached to a phosphate group. Each nucleic acid contains four of five possible nitrogen-containing bases: adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). Among these five bases, A and G are classified as purines and C, T, and U are characterised and collectively called as pyrimidines. All nucleic acids contain the bases Adenine, Cytosine, and Guanine and Thymine, however, T- thymine is found only in DNA, while U-uracil is found in RNA.
In the structure the pentose sugar is attached to one of the bases and is known as a nucleoside. The phosphate group joins consecutive sugar residues by linking the 5′-hydroxyl group on one sugar to the 3′-hydroxyl group of the next sugar in the chain series. These nucleotide linkages are called phosphodiester bonds and are the same in both RNA as well as in DNA.
Guanine is a type of nitrogenous base, which is a major constituent of nucleic acids and not guanidine.
Hence, the correct option is (B) Guanidine.

Note:
-Guanidine is colourless, crystalline, strongly base alkaline, and dissolves in polar solvent. It is mainly used in the manufacturing of plastics, resins, to produce rubber accelerators, and explosives etc.
-Whereas Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA. In DNA, guanine is linked with cytosine. The guanine nucleoside is called guanosine.