metabolites

Metabolites are small molecules that participate in metabolism. They include intermediates, end products, and byproducts of biochemical reactions. Metabolites are found in all living organisms and can be located inside cells or released into the extracellular space.

Classification helps describe their roles. Primary metabolites are essential for growth, development, and reproduction, and include amino acids, nucleotides, monosaccharides, organic acids, simple lipids, and many vitamins in their biosynthetic roles. Secondary metabolites are not strictly required for growth but serve ecological functions such as defense, signaling, and interactions with other organisms. Examples include alkaloids, terpenoids, and phenolics, as well as many antibiotics produced by microbes and plants.

Biosynthesis and function are coordinated by enzymes that regulate flux through pathways. Metabolites arise from catabolic processes that harvest energy and building blocks and anabolic processes that assemble complex molecules. Key pathways include glycolysis, the tricarboxylic acid cycle, the pentose phosphate pathway, and fatty acid oxidation. Metabolites can act as energy carriers (for example ATP and NADH), as signaling molecules, or as structural components of cells and biomolecules.

Physiology and research applications: The metabolome refers to the complete set of metabolites in a given biosample. Metabolite levels reflect genetic background, environmental conditions, and dietary inputs, and they change with disease or stress. Metabolomics uses technologies such as mass spectrometry and nuclear magnetic resonance spectroscopy to profile metabolites for biomarker discovery, drug development, nutrition research, and plant science.

Examples include glucose, pyruvate, acetyl-CoA, and amino acids in humans; plant secondary metabolites like caffeine, morphine, and taxol; and microbial antibiotics.