Question

In a DNA molecule, a nitrogenous base is linked to pentose sugar by 'A' linkage and the pentose sugar is linked to phosphate by 'B' linkage. Correctly identify A and B.

• A.

  Column A	Column B
  N-Glycoside linkage	Amide linkage

• B.

  Column A	Column B
  N-Glycoside linkage	Phosphoester linkage

• C.

  Column A	Column B
  Phosphoester linkage	Phosphoester linkage

• D.

  Column A	Column B
  Amide linkage	Phosphodiester linkage

Answer 1

Answer: (B)

Structure of polynucleotide chain
DNA = Polynucleotide.
Nucleotide = Nitrogenous base + Pentose sugar + Phosphate group.
As nitrogenous base and pentose sugar when linked, are also termed as nucleoside, so we can also say that : Nucleotide = Nucleoside + Phosphate group.
Linkages in a nucleotide molecule:
Nitrogenous base --(N-glycosidic linkage)-- Pentose sugar --(Phosphoester linkage)-Phosphate group. Phosphate group is linked to $5’-OH$ of a nucleoside through the phosphodiester linkage.