Happy Thursday!

1. Happy Thursday! Lets finish up some enzyme notes!!

2. Enzymes • Metabolic pathways consist of chains and cycles of enzyme catalyzed reactions • The products of the first reaction, become the reactants of the second reaction, and so on. • Enzymes catalyze each step. A -> B -> C -> D -> E

3. Induced Fit Model • Previously, you may have learned of the ‘lock and key’ model which states that each enzyme has an active site that fits perfectly with one specific enzyme

4. The more accurate and more modern induced fit model states that the active site is slightly different in shape from the substrate • the result is that the substrate’s chemical bonds are stressed and must therefore break and reform in another way (thus creating the product(s)) • this model explains why some enzymes can fit with more than one substrate

5. Enzymes work by lowering the activation energy of a chemical reaction • All reactions, either with or without enzymes, need collisions between molecules in order to occur • Many molecules have strong bonds holding them together, and as such require powerful collisions at high speed in order to break these bonds

6. However, increasing the rate of collision to a rate at which these reactions would occur would require prohibitive amounts of energy, usually in the form of heat • Enzymes, by stressing substrate bonds in such a way that a weaker collision is required to break them, reduce the amount of energy needed to cause these reactions to occur

8. Competitive and Non-competitive Enzyme Inhibition • Competitive inhibition occurs when an inhibiting molecule structurally similar to the substrate molecule binds to the active site, preventing substrate binding • Example: the inhibition of folic acid synthesis in bacteria by sulfonamide prontosil (an antibiotic)

9. Competitive Inhibition

10. Non-competitive inhibition occurs when an inhibitor molecule binds to a site on the enzyme called its allosteric site and causes a conformational change in its active site, resulting in a decrease in activity • Example: nerve gases like Sarin and DFP (diisopropyl fluorophosphate) inhibit the enzyme ethanyl (acetyl) cholinesterase

11. Non-competitive Inhibition

12. End-product inhibition • End-product inhibition • The product of a series of enzymatic reactions inhibits an enzyme from earlier in the chain • For example, in the series of reactions below an accumulation of end-product E inhibits the enzyme that helps to convert A to B A -> B -> C -> D -> E

13. End-product inhibition • form of non-competitive inhibition because the end product is binding to the allosteric site of enzyme used earlier in the metabolic pathway • Example: ATP can inhibit components of glycolysis.