ENZYMES

Enzymes are Catalysts Catalytic proteins: change the rate of reactions w/o being consumed Enzymes speed up reactions by lowering the activation energy Activation energy (free energy of activation) = the E required to break bonds Activation E must be reached for reaction to progress

What’s going on? Substrate: enzyme reactant Active site: pocket or groove on enzyme that binds to substrate Induced fit model Substrate fits into the enzyme which wraps around it

How does it work? Enzymes lower AE by: Bring together in proper orientation Physical stress- bending or stretching of chemical bonds Increased reactivity due to environment (charge, pH, etc. within active site) Activity of substrate directly w/ enzyme

Effects on Enzyme Activity Temperature pH Cofactors: inorganic, nonprotein helpers; ex.: zinc, iron, copper Coenzymes: organic helpers; ex.: vitamins

Enzyme Inhibitors Irreversible (covalent); reversible (weak bonds) Competitive: competes for active site (reversible); mimics the substrate Noncompetitive: bind to another part of enzyme (allosteric site) altering its conformation (shape) poisons, toxins, antibiotics

Allosteric Regulation Not all chemical processes occur at the same time Enzymes can be activated when needed and inhibited when they’re not Allosteric activators and inhibitors bind to turn the enzyme complex on or off Cooperativity- substrate must be bound to activate enzyme

Feedback Inhibition End product of reaction binds to allosteric site of enzyme to stop further production Like a thermostat