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Primary and Secondary Metabolites


The most exciting aspect of chemistry deals with isolating thousands of compounds (small and big) from living organisms, determining their structures, and if possible synthesising them.

Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, reproduction etc. For example, alcohol is a primary metabolite produced in large-scale by industrial microbiology.

A secondary metabolite is not directly involved in those processes, but usually has an important ecological function. Examples include antibiotics and pigments. Some antibiotics use primary metabolites as precursors, such as actinomycin which is created from the primary metabolite, tryptophan.

If one wants to make a list of biomolecules, such a list will have thousands of organic compounds including amino acids, sugars etc. These are called primary metabolites.

However, when one analyses plant, fungal and microbial cells, one will see thousands of compounds, eg., alkaloides, flavonoides, rubber, essential oils, antibiotics, coloured pigments, scents, gums, spices. These are called secondary metabolites.

While primary metabolites have identifiable functions and play known roles in normal physiological processes, we do not at the moment understand the role or function of all the 'secondary metabolites' in host organisms. However, many of them are useful to 'human welfare' (eg., rubber, drugs, spices, scents and pigments). Some secondary metabolites have ecological importance.

 

Some Primary Metabolites

Examples

Alcohol

Ethanol

Amino Acids

Glutamic Acid, Aspartic acid

Nucleotides

5' guanylic acid

Antioxidants

Isoasorbic acid

Organic Acids

Acetic Acid, Lactic Acid

Polyols

Glycerol

Vitamins

B2

 

Some Secondary Metabolites

Examples

Pigments

Carotenoids, Anthocyanins etc.

Alkaloids

Morphine, Codeine, etc.

Terpenoides

Monoterpenes, Diterpenes etc.

Essential oils

Lemon grass oil, etc.

Toxins

Abrin, Ricin

Lectins

Concanavalin A

Drugs

Vinblastin, curcumin, etc.

Polymeric substances

Rubber, gums, cellulose





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