Secondary metabolites are organic compounds that are not directly involved in the growth, development, or reproduction of an organism, but instead play other roles such as defense, signaling, or competition. They are produced by many different types of organisms, including plants, fungi, and bacteria.
Unlike primary metabolites, which are essential for the normal growth and development of an organism, secondary metabolites are often produced in response to environmental stress, such as nutrient limitation, competition, or predation. They are typically synthesized through complex biochemical pathways that are not well understood, and their structures and functions can vary widely.
Secondary metabolites have a wide range of biological activities and are important sources of natural products with potential applications in medicine, agriculture, and industry. For example, many secondary metabolites have antimicrobial, antiviral, or anticancer properties, and are used as antibiotics or chemotherapeutic agents. Other secondary metabolites are used as flavorings, fragrances, or pigments in the food and cosmetic industries.
Examples of secondary metabolites include alkaloids, terpenoids, flavonoids, phenolic compounds, and polyketides. Alkaloids are nitrogen-containing compounds found in plants, fungi, and animals, and include well-known compounds such as caffeine, nicotine, and morphine. Terpenoids are synthesized from isoprene units and include compounds such as carotenoids, steroids, and essential oils. Flavonoids and phenolic compounds are synthesized from the amino acid phenylalanine and have antioxidant and anti-inflammatory properties. Polyketides are synthesized by bacteria and fungi and include compounds such as antibiotics and antifungal agents.