ENZYMES

1. ENZYMES 1.4

2. Enzyme are _________________ catalysts. • Either tertiary or quaternary. • Names ususually end in ‘ase.’ • CATALYST: substance that _____________ a chemical reaction without being consumed in the process. • Reactants  products. Enzyme can be used again. • For chemical reaction to occur: bonds between reactant molecules break, rearrangement of atoms, new bonds form. • Reactants need to _______________ with enough _______________ and in the correct geometric ________________ for bond breaking to occur  transition state.

3. Activation Energies • All reactions possess an activation energy, EA. • Activation energy can be provided by: • Heat • Examples: • spark at a gas station. • Collision theory • Problem with heat as EA source? ___________________________________________. • Catalysts allow reactions to proceed at suitable rates at moderate temperatures by reducing the a ACTIVATION ENERGY EA barrier.

4. Catalysts do not affect the free energy change, ∆G • Does not change endergonic exergonic. • Only decreases the potential energy level of the transition state  more colliding reactants reach the transition state and become products. • Does not affect the position of equilibrium • Forward and reversed reactions are catalyzed at the same rate • Rate at which equilibrium is reached is increased.

5. SUBSTRATES • A substrate is the reactant that an enzyme acts on when it catalyzes a chemical reaction. • Substrate binds to particular site on enzyme to which it is attracted. • Very specific for substrate  will not even bind isomers.

6. MODEL OF ENZYME ACTIVITY • Active site: region where substrate binds. • Usually a pocket or groove. • As substrate comes close to active sites, ____________________ of substrate interact with _________________ of _____________ on enzyme. • Enzyme-substrate complex: substrate + enzyme • Interactions between substrate and enzyme causes a ___________________ change of the enzyme. • Induced-fit model  enzyme ‘accomodates’ • Substrates’ chemical bonds are stretched and bent  lowers the amount of energy needed to bring substrate to ‘transitional state.’ LOWERS THE ACTIVATION ENERGY!

8. Folded Paper & Paper Clip Analogy NOTE: ONE PAPER CLIP = ONE MONOMER TEAM 1: Make 3 polymers of 3 monomers each. No paper TEAM 2: Make 3 polymers of 3 monomers each. With paper WINNER: _________ How does the action of the paper enzyme relate to a real enzyme-catalyzed condensation reaction?

9. Factors Affecting the Rate of Enzyme Activity Temperature pH Concentration of substrate

10. Temperature • Reactions increase in speed with an increase in temperature (collision theory). • As temperature increases beyond a critical point, protein ______________ and loss of enzyme ____________ would occur. • Every enzyme has an optimal temperature at which it works best. • Human enzymes: around _____. • Some thermophiles: _____.

12. pH • Enzymes have pH at which they work best. • If environment is too acidic or basic, it may ___________________________ the enzyme. • Pepsin • Catalyzes hydrolysis of proteins in the stomach • There is HCl in the stomach  pH = 2 • Trypsin • Also hydrolyses proteins, but in the small intestine • Basic substance is secreted into small intestine  pH=8

14. Substrate Concentration As substrate concentration increases, more reactions can occur. However, as active sites become occupied, rate of reaction slows. A point called the ‘saturation’ (asymptote)is reached, in which all enzyme active sites are occupied. Reaction rate virtually constant: reaction can only occur when enzymes are vacant.

15. Cofactors and Coenzymes • Cofactors: nonprotein components, such as dissolved ions, that are needed for some enzymes to function. • Zinc and manganese ions. • Coenzymes: organic nonprotein cofactors that are needed for some enzymes to function. • Derivatives of many vitamins • May bind to active site with covalent bonds, or weakly to the substrate

16. Enzyme Inhibition • A variety of substances inhibit enzyme activity. • Some are poisons, some are used by cell to control enzyme activity. • Competitive Inhibitors • Similar to enzyme’s substrate • Bind to active site • Block normal substrate from binding • Reversible • Solution: increase concentration of enzyme’s substrate  compete. • Noncompetitive Inhibitors • Do not compete with substrate • Bind to another part of the enzyme  conformation change  change in shape of active site  enzyme loses affinity for substrate. • DDT: poison that inhibits enzymes of the nervous system

18. Allosteric Regulation • Cells control enzyme activity to coordinate cellular activities. • Restrict production of enzyme • Inhibiting the action of enzyme • Allosteric Sites • Receptor sites • Substances bound to it may inhibit or stimulate enzyme’s activity. • Usually in proteins in quaternary structure with several subunits and several active sites. • ALLOSTERIC REGULATORS: • Attach to allosteric sites using weak bonds. • ACTIVATORS: stabilizes protein conformation to keep active sites available. • ALLOSTERIC INHIBITOR: Stabilizes inactive form of enzyme • Noncompetitive inhibitors

20. FEEDBACK INHIBITION • Method used by cells to control metabolic pathways involving a series of sequential reactions. • Each reaction catalyzed by a specific enzyme. • A product formed later in the sequence of reaction steps ALLOSTERICALLY INHIBITS an enzyme that catalyzes a reaction occurring earlier in the process. • Reduces the production of the inhibitor  a product of the process. • As product used up, less inhibition. • Enzyme in active form again, but cycle continues. • RESULT: AMOUNT OF PRODUCT KEPT TIGHTLY CONTROLLED BY FEEDBACK INHIBITION PROCESS.

23. METABOLIC PROCESSES are also controlled by controlling where certain enzymes are in the cell. • Some in mitochondria ______________________ • Some are in chloroplasts _____________________ • Some in the golgi bodies: _____________________ • Some in lysosomes: __________________________ ETC.

24. Classwork/Homework Read pages 75-76 (Commercial and Industrial Uses of Enzyems) PPs 1-9