Secondary Metabolites

Secondary metabolites (SMs) are small organic molecules produced by an organism that — unlike primary metabolites such as carbohydrates, lipids, proteins and nucleic acids — are not strictly essential for the organism's own growth, development or reproduction. Many bacteria, fungi and plants produce secondary metabolites.

Secondary metabolites can be classified in several ways — by chemical structure (e.g. whether they contain rings or sugars), by composition (whether or not they contain nitrogen), by their solubility in different solvents, or by the biosynthetic pathway that produces them (e.g. the phenylpropanoid pathway, which produces tannins). A simple, widely used scheme groups them into three main classes:

1. Terpenes — built from mevalonic acid, and composed mainly of carbon and hydrogen.
2. Phenolics — built from simple sugars, containing benzene rings along with hydrogen and oxygen.
3. Nitrogen-containing compounds — a highly diverse class that may also contain sulphur.

Economic importance of secondary metabolites:

1. Secondary metabolites from natural sources have made enormous contributions to human welfare for millennia; in modern medicine, drugs derived from them are used to treat infectious disease, cancer, hypertension and inflammation.
2. Morphine, the first alkaloid ever isolated from a plant (Papaver somniferum, the opium poppy), is used as a pain reliever and cough suppressant.
3. Secondary metabolites such as the alkaloids nicotine and cocaine, and the terpene cannabinol, are widely (and often problematically) used for their stimulant or recreational effects.
4. Many secondary metabolites contribute the characteristic flavours that shape our food preferences. …