Biochemical Pathways Involved in the Decomposition of Complex Organic Substances

Abstract

The decomposition of complex organic substances such as cellulose, hemicellulose, lignin, proteins, lipids and aromatic compounds is a central process in the global carbon and nitrogen cycles. It is carried out mainly by bacteria, fungi and archaea that secrete specialized enzymes and operate interconnected catabolic pathways. This article reviews the biochemical routes through which large polymeric molecules are depolymerized, converted into small intermediates and finally oxidized to carbon dioxide or reduced to methane. The roles of extracellular hydrolases and oxidoreductases, the degradation of lignin by peroxidases and laccases, proteolysis and nitrogen mineralization, lipid beta-oxidation, aromatic ring cleavage and anaerobic fermentation are described in detail. Environmental controls such as temperature, moisture, oxygen availability and substrate chemistry are discussed, together with applications in composting, biofuel production and waste management. Understanding these pathways at molecular level provides a basis for improving bioremediation, enhancing soil fertility and developing efficient biorefinery processes.