Which type of linkage is present between the two nucleotides?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Phosphodiester linkage
A nucleotide has three parts: a nitrogenous base, a pentose sugar and a phosphate group attached at the 5′-carbon of the sugar. In a nucleic acid chain, the phosphate group of one nucleotide is also joined to the 3′-carbon of the sugar of the next nucleotide.
The phosphate is thus bonded to two sugar units through two ester bonds (5′ and 3′), and the link is called a phosphodiester linkage.
Why the other options are incorrect
Option (2) Phosphate linkage — Incorrect. The bond between one sugar and its phosphate inside a single nucleotide is a single (mono) ester bond; the link between two nucleotides involves two ester bonds, so it is a phosphodiester linkage.
Option (3) \(α\)-linkage — Incorrect. α-Glycosidic linkages join monosaccharide units in carbohydrates such as maltose and starch.
Option (4) \(β\)-linkage — Incorrect. β-Glycosidic linkages join units in lactose and cellulose; in a nucleotide the base is joined to the sugar by a glycosidic bond, but nucleotides are not joined to each other this way.
NCERT (2026-27 edition):
Structure of Nucleic Acids – “… Nucleotides are joined together by phosphodiester linkage between 5′ and 3′ carbon atoms of the pentose sugar.”