Introduction to Metabolism

Metabolism encompasses all biochemical reactions in a living organism, facilitating both the breakdown and synthesis of biomolecules. These metabolic processes are categorized into catabolic and anabolic pathways, which operate in a coordinated manner to ensure energy balance and cellular function.

Catabolic Pathways and Energy Release

Catabolic pathways involve the breakdown of complex macromolecules such as carbohydrates, lipids, and proteins into smaller structures like monosaccharides, fatty acids, and amino acids. These reactions release energy, primarily stored in the form of adenosine triphosphate (ATP), which serves as a universal energy currency in cells. Cellular respiration, including glycolysis, the Krebs cycle, and oxidative phosphorylation, is a key catabolic process that generates ATP from glucose through a series of redox reactions.

Anabolic Pathways and Biosynthesis

Anabolic pathways consume ATP to drive the synthesis of essential biomolecules. These reactions facilitate the formation of structural and functional macromolecules, including proteins from amino acids, nucleic acids from nucleotides, and polysaccharides from monosaccharides. Anabolism is crucial for growth, tissue repair, and cellular differentiation, ensuring the maintenance and expansion of biological systems.

Amphibolic Pathways: A Dual Role

Some metabolic pathways, such as the Krebs cycle, serve both catabolic and anabolic functions and are thus termed amphibolic. In catabolism, the Krebs cycle oxidizes acetyl-CoA to produce ATP, NADH, and FADH₂. Simultaneously, it provides precursor molecules like ⍺-ketoglutarate and oxaloacetate for biosynthetic pathways, supporting the synthesis of amino acids, nucleotides, and other essential biomolecules.

Regulation of Metabolism

Metabolic homeostasis is achieved through enzyme regulation, with feedback inhibition playing a central role. In this mechanism, the accumulation of an end product inhibits an upstream enzyme, preventing excessive product formation and conserving resources. Additionally, allosteric regulation, covalent modifications, and hormonal control (e.g., insulin and glucagon) fine-tune metabolic flux to meet cellular demands.

The integration of catabolic and anabolic processes, along with precise regulatory mechanisms, ensures that organisms efficiently manage energy resources while maintaining homeostasis.