ENZYMES Biological Catalysts 1

ENZYMES ENZYMES are important proteins Many chemical reactions in living cells (and organisms) are regulated by ENZYMES Enzymes are globular proteins in living systems that mediate metabolic reactions Metabolism: the series of energy exchanges and chemical reactions that occur in living systems (cells, organisms) catabolic activities = breakdown of larger molecules into smaller; AB ==> A + B anabolic activities = synthesis of larger molecules from smaller ones; A + B ==> AB 2

Energy and Chemical Reactions Exergonic rxn’s = release energy (products have less chemical energy than reactants) ex: AB + CD  AC + DB + energy 3

Energy and Chemical Reactions Endergonic rxn’s = absorb energy (products have more chemical energy than reactants) ex: AB + CD + energy  AC + DB Catalysts: reduce the amount of activation energy that is needed to start the rxn. See Figure 2-7 in your book. 4 Activation energy: energy added to reactants to "jumpstart" the rxn

Enzymes act as catalysts (push, or speed up, chemical reactions) Enzymes lower the ACTIVATION ENERGY of reactions (ex: heat required) needed to enable chemical bonds to form or break Reactions that involve enzymes occur more easily than they normally would. 5

Each Enzyme acts upon a specific substrate (there are thousands of different enzymes in the body to mediate thousands of different reactions) Enzymes have an active site, to fit with their substrate in a "lock- and-key" fashion Sometimes, to get a good "fit", enzymes require a vitamin or mineral to fit into the active site: COENZYME "Induced Fit Hypothesis" a change in the shape of an enzyme’s active site may occur, which allows it to bind more effectively to its substrate 6

Enzymes mediate the reaction in the substrate but do not take part in the reaction themselves, so enzymes can be re-used again and again Enzymes can be deactivated (DENATURED) when their 3-D active site is warped by heat or drastic pH changes (acid) Some classes of enzymes: – Proteases – Lipases – Amylases (sucrase, lactase, etc.) most enzyme names end in -ane or -ase suffix, and most are named after the substrate upon which they act 7

LAB Enzyme: catalase Reaction it catalyzes: 8