Biomolecules – Nucleosides & Nucleotides

Nucleosides: Nucleoside contains only two basic components of nucleic acids (a pentose sugar and a nitrogenous base). During their formation, 1- position of pyrimidine or 9 – position of purine moiety is linked to C₁ of sugar (ribose or deoxyribose) by b – linkage.

General structure of a nucleoside

Depending upon the type of sugar present, nucleosides are of two types:

(i) Ribonucleosides and

(ii) Deoxyribonucleosides

Nucleotides: Nucleotides contains all the three basic components of nucleic acids. Nucleotides are nucleoside monophosphates.

They are of two types depending upon the type of sugar – Ribonucleotides and Deoxyribonucleotides. Nucleotide may be represented as follows.

	DNA		RNA
1.	Sugar present in DNA is 2-deoxyribose.	1.	Sugar is D-ribose.
2.	It contains cytosine and thymine as pyrimidine.	2.	It contains cytosine and uracil as pyrimidine.
3.	It has double stranded a – helix structure.	3.	It has single stranded a – helix.
4.	DNA occurs in the nucleus of cell.	4.	RNA occurs in cytoplasm of the cell.
5.	Controls transmission of hereditary material.	5.	It control the synthesis of proteins.