Describe the structure of a RNA polynucleotide chain having four different types of nucleotides.

A RNA nucleotide contains three main components- a nitrogenous base, a ribose sugar and a phosphate group.

1. Due to sugar and phosphates, the backbone in a polynucleotide chain is formed. The nitrogenous bases linked to the sugar moiety project from the backbone.

2. Two types of nitrogenous bases are present i.e. Purines- (Adenine (A) and Guanine (G)) and Pyrimidines-
(Cytosine (C) and Uracil (U)).

3. A nitrogenous base is linked to the ribose sugar through N-glycosidic linkages to form a nucleoside (like adenosine, guanosine or cytidine and uridine).

4. A corresponding nucleotide is formed due to a phosphate group is linked to 5’-OH of a nucleoside through phosphoester linkage.

5. To form the polynucleotide chain, many nucleotides are linked through 3’ -5′ phospho-diester linkages to each other.

6. Every nucleotide residue has an additional -OH group present at 2’ -position in the ribose.

7. The end of the chain which has a free phosphate moiety at 5′-end of ribose sugar is referred to as 5’ – end and the other end of the chain having a free 3’ – OH group at the ribose sugar is referred to as 3′- end of the polynucleotide chain.