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.

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.


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