Terpenoids
Introduction
Terpenoids, also known as isoprenoids, are a large and diverse class of naturally occurring organic chemicals derived from the five-carbon compound isoprene. They are found in all classes of living things and are the largest group of natural products. Terpenoids play key roles in plant growth and development, mediating defensive responses to herbivory and providing an array of ecological benefits.
Classification
Terpenoids are classified based on the number of isoprene units in the molecule. Monoterpenes have two isoprene units and are the basic building blocks of terpenoids. Sesquiterpenes consist of three isoprene units, and diterpenes have four. Triterpenes, which contain six isoprene units, are used to build steroids and sterols. Tetraterpenes contain eight isoprene units and include the carotenoids. Polyterpenes consist of long chains of many isoprene units.
Biosynthesis
Terpenoids are synthesized in plants through the mevalonate pathway or the MEP/DOXP pathway. The mevalonate pathway, also known as the HMG-CoA reductase pathway, is an important cellular metabolic pathway present in all higher eukaryotes and many bacteria. The MEP/DOXP pathway is a non-mevalonate pathway that occurs in most bacteria, plant plastids and some protozoa.
Functions and Uses
Terpenoids perform a wide variety of functions in the biochemistry of plants and animals. They are involved in the synthesis of vitamins and hormones, serve as antioxidants, and are key components of cellular membranes. In plants, terpenoids are involved in growth and development, and in defense against herbivores and pathogens.
Terpenoids have a wide range of uses in industry. They are used in the manufacture of pharmaceuticals, cosmetics, and in the food industry as flavorings and fragrances. Some terpenoids are used in traditional medicine and have been found to have antibacterial, antifungal, antiviral, anticancer, and anti-inflammatory properties.