Enzymes Section 1.4

Enzymes Enzymes are protein catalysts, most of which end in -ase. A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. Catalysts allow reactions to proceed at suitable rates at moderate temperature by reducing the activation energy(EA) barrier. Do H2O2 + KI demo

Catalysts do not affect free energy change of reactions; the difference in energy btwn products and reactants is the same.

The substrate is the reactant that an enzyme acts on when it catalyzes a chemical reaction. The location where the substrate binds to the enzyme is called the active site and is usually a depression in the three-dimensional structure of the protein which is highly specific to the substrate (ex isomers will not bind!). The attachment of the substrate to the enzyme’s active site creates the enzyme-substrate complex.

How Enzymes Work Biochemical Pathways

Catalytic Cycle

Enzymes are named according to their function. ex: fat hydrolyzing enzymes are called lipases Temperature and pH levels affect enzyme activity. Some enzymes require cofactors (ex: zinc ions) or coenzymes (ex:vitamin B) before they can work properly. These substances can bind either to the active site or to the substrate to assist the function of the enzyme. Cells must control enzyme activity to coordinate cellular activity. Inhibitors can block an enzyme’s active site or change the shape of the enzyme thus affecting enzyme activity.

Enzyme Cartoon

Homework: Questions page 77 # 1-8