What Is a Nucleotide?

An organic molecule that constitutes the backbone of nucleic acid composed of a purine or pyrimidine base, linked to a sugar ribose or deoxyribose and a phosphate group. Besides the nucleosides which occur as integral part of DNA and RNA, there are many biologically important nucleotides present in tissues and cells.

Nucleotides: Nucleosides + Phosphate

The hydroxyl group of the 5 carbon of the sugar is phosphorylated by ester bond formation. The nucleotides are also called as nucleoside monophosphates. The nucleotides are classified as Adenosine nucleotides, Guanosine nucleotides, Uridine nucleotides, cytidine nucleotides, cyclic nucleotides etc.

The biological importance of nucleotides are
1.Polymers of nucleotides are the nucleic acids — DNA and RNA
2.Higher nucleotides like ATP/GTP are high energy compounds.
3.Nucleoside monophosphates form part of coenzymes like FAD, NAD+, NADP+ and coenzyme A.
4.Cyclic nucleotides acts as second messengers in the signal transduction of hormones.
5.Nucleotide diphosphates act as carrier molecules.
6.Nucleotides act as allosteric modulators of metabolic pathways. For example, enzyme phosphofructokinase of glycolysis has AMP as positive modulator and ATP as negative modulator.
7.Synthetic derivatives of nucleotides act as anticancer drugs. For example 5-fluorouracil.