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