A nitrogenous base is linked to the OH of __________ through a N-glycosidic linkage to form a nucleoside.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 1′C pentose sugar
A nucleoside is a nitrogenous base joined to a pentose sugar. The base is linked to the OH group of the 1′ carbon of the sugar through an N-glycosidic linkage. When a phosphate group is then linked to the OH of the 5′ carbon (phosphoester linkage), the nucleoside becomes a nucleotide.
(1) 3′C pentose sugar — Incorrect. The 3′ OH of one nucleotide joins the 5′ phosphate of the next through a 3′-5′ phosphodiester linkage to form the chain.
(2) 1′C pentose sugar — Correct. The base sits on the 1′ carbon.
(3) 5′C pentose sugar — Incorrect. The phosphate, not the base, is attached at the 5′ carbon.
(4) 2′C pentose sugar — Incorrect. The 2′ carbon carries an OH group in ribose (RNA) and only H in deoxyribose (DNA). The base is not joined here.
Note: The same question was also asked in CUET (UG) 2026 on 26-05-2026 (Slot 1), and a similar question in CUET (UG) 2026 on 22-05-2026 (Slot 1).
NCERT Extract:
Structure of Polynucleotide Chain – …
