Structure of a polynucleotide chain.

Before starting with the structure of polynucleotide chain, you must have to get the knowledge on :

1. Nucleotides.
2. Base pairs.
3. DNA vs RNA.
4. Pentose Sugar.
5. And, the phosphate group.

Linkages term means bonds between atoms, compound or chains.
A Polynucleotide chain shows following types of linkages or bond in its compound :

(i) N-glycosidic linkage : 

= In biochemistry, a glycosidic bond or linkage is like an covalent bond that joins a sugar molecule to another group, which may or may not be another sugar.

= N-base is linked to the pentose sugar through a N-glycosidic linkage to form a nucleoside. 

= Pure nucleosides have 1'-9 glycosidic linkage (carbon 1' of sugar and 9 position of A/G).

= Pyrimidine nucleosides have 1'-1 linkage i.e., sugar carbon 1' and 1 position of T/C.

A Nucleoside and the N-Glycosidic Linkage

(ii) Phosphoester linkage : 

=  A type of covalent bond that links two C-atoms through a phosphate group.

= When a phosphate group (PO₄^2-) is linked to 5'-OH of a nucleoside  through phosphoester linkage a             corresponding nucleotide is formed.

= Two nucleotides are linked through 3'-5' phosphodiester linkage to form a dinucleotide.

Nucleotide

Dinucleotide going to be formed

A polymer thus formed has a free phosphate moiety at 5'-OH, which is referred as 5'-end of polynucleotide chain.

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