The correct sequence of attachment of sugar, base and phosphoric acid in a nucleic acid is
(A) Formation of phosphodiester linkage
(B) Attachment of base to 1' position of sugar
(C) Selection of appropriate base and sugar
(D) Attachment of phosphoric acid
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (C), (B), (D), (A)
(C) Selection of appropriate base and sugar: the first step — ribose with A, G, C, U for RNA, or deoxyribose with A, G, C, T for DNA.
(B) Attachment of base to 1′ position of sugar: this gives the nucleoside.
(D) Attachment of phosphoric acid: at the 5′-position of the sugar, giving the nucleotide.
(A) Formation of phosphodiester linkage: between the 5′ and 3′ carbon atoms of the sugars of neighbouring nucleotides, building the chain.
Shortcut: The parts must be chosen first and the chain joined last. Only Option (1) starts with (C) and ends with (A).
NCERT (2026-27 edition):
Structure of Nucleic Acids – “A unit formed by the attachment of a base to 1′ position of sugar is known as nucleoside. In nucleosides, the sugar carbons are numbered as 1′, 2′, 3′, etc. in order to distinguish these from the bases. When nucleoside is linked to phosphoric acid at 5′-position of sugar moiety, we get a nucleotide. Nucleotides are joined together by phosphodiester linkage between 5′ and 3′ carbon atoms of the pentose sugar.”