Which of following linkages are present in nucleic acids?

The correct answer is Option (2) → Phosphodiester Linkage

Note: The given answer is as per the official NTA Answer Key. However, there is more than one correct option for this question, as explained below.

• Option (2) Phosphodiester Linkage — Correct. The nucleotides are joined to one another by phosphodiester linkages, which form the backbone of the chain.

• Option (1) Glycosidic Linkage — Is also correct. In every nucleotide the base is joined to C-1′ of the sugar by an N-glycosidic linkage, so this linkage is also present in nucleic acids.

Nucleic acids (DNA and RNA) are built up in three stages:

• Nucleoside = base + pentose sugar; the base is attached at the 1′ position of the sugar (β-D-2-deoxyribose in DNA, β-D-ribose in RNA).

• Nucleotide = nucleoside + phosphoric acid, esterified at the 5′ position of the sugar.

• Nucleic acid = nucleotides joined by phosphodiester linkages between the 5′ and 3′ carbon atoms of the sugar units of neighbouring nucleotides.

So the linkage that joins the units into the nucleic acid chain is the phosphodiester linkage, which is the answer given by NTA.

Why the other options are incorrect

• Option (3) Peptide Linkage — Incorrect. The –CO–NH– linkage joins amino acids in proteins.

• Option (4) Disulfide Linkage — Incorrect. The –S–S– linkage between cysteine units stabilises the structure of proteins.

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. … When nucleoside is linked to phosphoric acid at 5′-position of sugar moiety, we get a nucleotide (Fig. 10.5).”

“Nucleotides are joined together by phosphodiester linkage between 5′ and 3′ carbon atoms of the pentose sugar. …”