8.4 Introduction to Metabolism

Metabolism is the engine of life, powering everything from energy production to waste elimination. It's a complex network of chemical reactions that keep organisms alive, involving both building up and breaking down molecules.

Enzymes are the unsung heroes of metabolism, speeding up reactions and fine-tuning pathways. Energy transfer is key, with ATP serving as the cellular currency and redox reactions driving crucial processes like the electron transport chain.

Fundamentals of Metabolism

Role of metabolism in life

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• Metabolism encompasses chemical reactions in living organisms sustaining life processes converting nutrients into energy and building blocks
• Key functions involve energy production fueling cellular activities, biomolecule synthesis creating essential compounds, and waste elimination maintaining cellular health
• Homeostasis maintenance regulates body temperature keeping organisms within optimal range, pH balance ensuring proper enzyme function, and nutrient levels supporting cellular processes

Anabolic vs catabolic processes

• Anabolic processes build complex molecules from simpler ones require energy input (protein synthesis, DNA replication, glycogenesis)
• Catabolic processes break down complex molecules into simpler ones release energy (glycolysis, fatty acid oxidation, protein degradation)

Enzymes in metabolic reactions

• Enzymes act as biological catalysts accelerate chemical reactions by lowering activation energy
• Specificity follows lock and key model or induced fit model ensuring precise substrate binding
• Enzyme kinetics described by Michaelis-Menten equation influenced by temperature, pH, and substrate concentration
• Regulation occurs through allosteric regulation, feedback inhibition, and covalent modification fine-tuning metabolic pathways

Energy transfer in biological systems

• ATP serves as energy currency with structure allowing hydrolysis to release energy driving ATP-ADP cycle
• Redox reactions involve oxidation (loss of electrons) and reduction (gain of electrons) utilizing electron carriers (NAD+/NADH, FAD/FADH2)
• Coupled reactions link endergonic reactions to exergonic reactions enabling energetically unfavorable processes
• Free energy and spontaneity determined by Gibbs free energy change ($\Delta G$) relates to equilibrium constant
• Electron transport chain conducts series of redox reactions generates proton gradient drives ATP synthesis via chemiosmosis