Metabolism refers to the sum of all chemical reactions occurring within an organism that allow it to maintain life, grow, reproduce and respond to its environment.
Explanation
Metabolic reactions are organized into pathways that extract energy from nutrients and use that energy to build and maintain cellular structures. Catabolic processes break down complex molecules such as carbohydrates, lipids and proteins into simpler compounds, releasing energy in the form of ATP and reducing equivalents. Key catabolic pathways include glycolysis, the citric acid cycle and oxidative phosphorylation. Anabolic pathways use energy and precursors generated by catabolism to synthesize macromolecules like nucleic acids, proteins, polysaccharides and lipids. Together, these reactions enable cells to grow, divide and adapt to changing conditions. Enzymes catalyze metabolic reactions with high specificity, and their activities are regulated by feedback mechanisms, allosteric effectors and hormonal signals to balance energy supply with demand. Metabolic flux also depends on the availability of nutrients, oxygen and cofactors, and is integrated with signaling pathways that sense the internal and external environment. In microorganisms, metabolic diversity extends to unique pathways such as fermentation, photosynthesis and methanogenesis, reflecting adaptation to different ecological niches. Disruptions in metabolic homeostasis can lead to diseases including diabetes, obesity and inherited metabolic disorders.
Key Processes and Significance
- Catabolism: breakdown of glucose via glycolysis and the citric acid cycle yields ATP and precursors for biosynthesis.
- Anabolism: synthesis of amino acids, nucleotides and lipids from simple precursors consumes ATP and reducing power.
- Energy currencies: ATP, NADH, NADPH and FADH2 transfer energy and electrons between reactions.
- Regulation: hormones and signaling molecules adjust metabolic pathways to maintain homeostasis in response to nutrients and stress.
Metabolism is the chemical engine of life, converting matter and energy to sustain growth and functions. Understanding metabolic pathways provides insight into physiology, disease mechanisms and opportunities for biotechnology and therapeutics.
Related Terms: Catabolism, Anabolism, ATP, Enzyme, Homeostasis