Metabolism: Concepts, Pathways, and Regulation

Concept of Metabolism

Metabolism encompasses all chemical reactions occurring within living cells, providing energy and synthesizing new organic material. It involves both the breakdown (catabolism) and synthesis (anabolism) of biomolecules.

Anabolic and Catabolic Pathways

Anabolic pathways require energy to synthesize complex molecules from simpler ones, such as synthesizing sugar from CO2 or proteins from amino acids. These processes are essential for cell growth and require energy from ATP and other high-energy molecules.

Catabolic pathways involve the breakdown of complex molecules into simpler ones, releasing energy stored in molecular bonds. This energy is harvested to produce ATP and other energy-storing molecules.

Regulation of Metabolism

Cells regulate enzyme activity through various mechanisms:

Feedback Inhibition

Reaction products inhibit further enzyme activity to maintain chemical equilibrium and meet cellular demands. For example, ATP inhibits its own production through feedback inhibition.

Competitive and Noncompetitive Inhibition

Competitive inhibition occurs when an inhibitor molecule binds to the enzyme’s active site, preventing substrate binding. Noncompetitive inhibition occurs when an inhibitor binds to an allosteric site, altering the enzyme’s shape and reducing its catalytic activity.

Enzyme Compartmentalization

In eukaryotic cells, enzymes are compartmentalized into organelles, contributing to enzyme regulation by isolating specific cellular processes.

Role of Regulatory Enzymes

Regulatory enzymes control biochemical pathways by responding to the presence of other biomolecules:

  • Feedback inhibition: Regulates product levels by inhibiting enzyme activity.
  • Kinases and phosphatases: Modify enzymes through covalent modifications, affecting their activity.
  • Proteolysis: Activates proteins involved in metabolism, such as digestive enzymes and hormones.