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  4. 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.

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Q. 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.

NTA AbhyasNTA Abhyas 2022

Solution:

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.