Biochemical reactions

ENZYMES Tertiary and quaternary proteins with complex conformations Contain specific active site(s) that substrates are attracted to Shape and function of an active site is determined by the primary structure of the protein Enzymes have specific conditions in which they work best Ex: Temperature and pH

ENZYMES SUBSTRATE: the reactant that an enzyme acts on when catalyzing a chemical reaction

Enzymes

ENZYMES BIND WITH A SUBSTRATE ENZYME-SUBSTRATE COMPLEX: the combined structure of an enzyme with a substrate that is bound to the enzyme’s active site - Enzymes can adjust their shapes to accommodate substrates (Induced Fit) - Intermolecular bonds form between the enzyme and substrate as the shape is adjusted

ENZYMES BIND WITH A SUBSTRATE COENZYMES: organic molecules that assist an enzyme COFACTORS: metal ions (Ex: iron or zinc) which are required by some coenzymes

Enzymes bind with a substrate Enzymes can prepare substrates for reaction Active sites have amino acid R groups that cause substrate bonds to stretch or bend allowing them to break easily Active sites bring two substrates together in the correct position Active sites transfer electrons to or from the substrate which destabilizes it Active sites add or remove H+ to or from the substrate *** Each of these actions lower the activation energy of the reaction ***

ENZYMES CATALYZE BIOLOGICAL REACTIONS BIOLOGICAL CATALYST: special proteins that lower the activation energy required for a chemical reaction to proceed - Not consumed in the reaction (Ex. Reuseable) - Does not change the free energy change of a reaction - It can only lower the amount of potential energy of the transition state - The rate of reaction (amount of effective collisions) is increased in the forward and reverse directions - Equilibrium is reached more rapidly

ENZYMES Exergonic Reaction: Energy is released

ENZYMES Endergonic Reaction: Energy is absorbed

ENZYME CLASSIFICATION Enzymes are classified according to the type of reaction they catalyze (since enzymes are specific in the reactions they catalyze) First part of substrate name + “-ase” Ex: Hydrolase cleaves glycosidic linkages in lactose

ENZYME CONTROL (INHIBITION) Two types of inhibition exist: Competitive Inhibition Non-competitive Inhibition (Allosteric Inhibition)

ENZYME CONTROL (INHIBITION) COMPETITIVE INHIBITION A substance that is not the substrate but is able to fit in the active site blocks the normal substrate from binding

ENZYME CONTROL (INHIBITION) NONCOMPETITIVE INHIBITION A substance that binds an enzyme and changes its shape so that the active site no longer accepts the substrate ALLOSTERIC INHIBITION/REGULATION Some enzymes have receptor sites known as allosteric sites An ACTIVATOR can bind the allosteric site and maintain the enzyme’s activity by stabilizing the enzyme in its active form An INHIBITOR may bind the allosteric site and inactivate the enzyme by stabilizing the inactive form

ENZYME CONTROL (INHIBITION)

ENZYME CONTROL (INHIBITION) Ex: Feedback Inhibition A product of a metabolic pathway allosterically Inhibits an enzyme earlier in the pathway and, Therefore, the production of the product