biosynthesis

biosynthesis

the formation of complex compounds from simple substances by living organisms

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Biosynthesis

The synthesis of more complex molecules from simpler ones in cells by a series of reactions mediated by enzymes. The overall economy and survival of the cell is governed by the interplay between the energy gained from the breakdown of compounds and that supplied to biosynthetic reaction pathways for the synthesis of compounds having a functional role, such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and enzymes. Biosynthetic pathways give rise to two distinct classes of metabolite, primary and secondary. Primary metabolites (DNA, RNA, fatty acids, α-amino acids, chlorophyll in green plants, and so forth) are essential to the metabolic functioning of the cells. Secondary metabolites (antibiotics, alkaloids, pheromones, and so forth) aid the functioning and survival of the whole organism more generally. Unlike primary metabolites, secondary metabolites are often unique to individual organisms or classes of organisms. See Enzyme, Metabolism

The selective pressures that drive evolution have ensured a diverse array of secondary metabolite structures. Secondary metabolites can be grouped to some extent by virtue of their origin from key biosynthetic pathways. It is often in the latter stages of these pathways that the structural diversity is introduced. All terpenes, for example, originate from the C₅ (five-carbon) intermediate isopentenyl pyrophosphate via mevalonic acid. The mammalian steroids, such as cholesterol, derive from the C₃₀ steroid lanosterol, which is constructed from six C₅ units. Alternatively, C₁₀ terpenes (for example, menthol from peppermint leaves) and C₁₅ terpenes (for example, juvenile hormone III from the silk worm) are derived after the condensation of two and three C₅ units, respectively, and then with further enzymatic customization in each case. See Cholesterol, Organic evolution, Steroid