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# Enzymes ## Metabolism * In living organisms, a sum of chemical reactions occurring. * Anabolic & catabolic reactions build and break down molecules. * Reactions may be intracellular or extracellular. ## Enzymes * Globular proteins that act as catalysts. * Speed up biochemical reactions. * Form...

# Enzymes ## Metabolism * In living organisms, a sum of chemical reactions occurring. * Anabolic & catabolic reactions build and break down molecules. * Reactions may be intracellular or extracellular. ## Enzymes * Globular proteins that act as catalysts. * Speed up biochemical reactions. * Formed by a long polypeptide chain folded into a 3D structure. * Active site region in each enzyme where substrates bind. * Follow "lock and key" hypothesis. * Substrates bind to active site. * Bonds form/break to form new substances. ## Affecting Enzyme Action * **Temperature:** Optimal temp. in human body is 37°C. * Lower temps. slow reaction rates as molecules lack sufficient kinetic energy for collisions. * Higher temps. denature enzymes. * **pH:** * Acidic solutions (low pH) can disrupt enzyme function by affecting active site charges. * **Substrate Concentration:** * Higher substrate concentration leads to more collisions and faster reactions. * Competitive inhibitors may outcompete the substrate at high concentration. ## Activation Energy * The minimum energy required to initiate a metabolic reaction. * Enzymes reduce this energy by enabling substrate molecules to reach the unstable transition state more easily, which produces products. ## Competitive Inhibition * A competitive inhibitor has a structure similar to substrate. * Competes with substrate for the active site. * Presence reduces reaction rate because active sites are now occupied - reducing effective substrate access * Inhibitor does not affect the reaction, but the binding to the active site is temporary. * Affected by substrate concentration; high substrate concentration can outcompete inhibitor. ## Examples * Oxygen (O₂) competes with carbon dioxide (CO₂) for the active site in ribulose biphosphate carboxylase (an enzyme involved in photosynthesis).