1. Enzymes Catalyze (speed up) reactions Recognize and bind specific substrates Act repeatedly Most are proteins Reaction does not alter them

2. Activation Energy For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller activation energy without enzyme activation energy with enzyme energy released by the reaction products starting substance

3. Fig. 4-6, p.62 reactants products energy barrier with no enzyme to promote reaction energy barrier with an enzyme’s participation Activation Energy

4. Factors Influencing Enzyme Activity Coenzymes and cofactors Allosteric regulators Temperature pH Salt concentration

5. Allosteric Control Activator or inhibitor binds to an enzyme Binding changes enzyme shape Change hides or exposes active site

6. allosteric activator allosteric binding site vacant active site altered, substrate can bind substrate cannot bind enzyme active site Allosteric activation allosteric inhibitor allosteric binding site vacant; active site can bind substrate active site altered, can’t bind substrate Allosteric inhibition Stepped Art Fig. 4-8, p.64

7. enzyme 1 enzyme 2enzyme 3enzyme 4enzyme 5 end product (tryptophan) substrate Excess molecules of end product bind to molecules of an enzyme that catalyzes this pathway’s first step. The greater the excess, the more enzyme molecules are inhibited, and the less tryptophan is synthesized. Feedback Inhibition Product of pathway binds to and inhibits enzyme in the pathway

8. Effect of Temperature Small increase in temperature increases molecular collisions, reaction rates High temperatures disrupt bonds and destroy the shape of active site

9. Enzymes and the Environment