2. Enzymes and Metabolism Chapter 4

3. Chemical Reactions First Law of Thermodynamics –Matter and energy cannot be created or destroyed, but can be converted from one form to another Second Law of Thermodynamics –As energy is transformed from one form to another, the universe becomes increasingly disorganized

4. Chemical Reactions Order = Free Energy All chemical reactions must involve a loss in free energy Change in free energy during a chemical reaction depends upon… 1.Particular energetic properties of the reactant(s) vs. that of the product(s) 2.The concentration of the reactants(s) relative to that of the product(s)

5. Reversible vs. Irreversible Reactions Reversible reaction –Intrinsic energetic properties of the reaction differ little between converting reactants into products and converting products into reactants –Relative ratio of products vs. reactants determines net tendency for the reaction to go one way vs. another. –Equilibrium – point where rate of reaction proceeding in one direction is equal to the rate the reaction [Reactant][Product]

6. Reversible vs. Irreversible Reactions Irreversible reaction –Intrinsic energetic properties of the reaction greatly favor conversion of reactants into products –Reactants converted to product even if there is very little reactant and lots of product.

7. Enzymes Protein Catalysts Enzymes = Protein Catalysts speed up the rate of chemical reactions are not permanently altered in the reactions do not change the nature of the reaction –Change in free energy and equilibrium point will be the same

8. How do enzymes speed up reactions? Lower the activation energy for a reaction –amt of energy needed to get the reaction going Enzymes bind reagents (substrates) –orient them so that less energy is needed to get the reaction going

9. Enzymes catalyze specific reactions Have Complex 3-D structures Pockets act as active sites –bind specific substrates –catalyze specific chemical reaction –produce specific products E + S  E-S Complex  E + P

10. Enzyme Names Names of enzymes typically indicate function: –lactate dehydrogenase – removes hydrogen from lactate –phosphatase – removes phosphate groups from different organic compounds Some do not have descriptive names –chymotrypsin - hydrolyzes peptide bonds –ptyalin – hydrolyzes glycosidic bonds

11. Factors Affecting Enzyme Activity Concentration of Enzyme –  Enzyme,  Rate Concentration of Substrate –  Substrate,  Rate –  in rate limited by amount of enzyme may saturate the enzyme [E] Reaction Rate

12. Factors Affecting Enzyme Activity Concentration of Cofactors/Inhibitors –Cofactors - additional substances needed to catalyze reactions Inorganic ions Coenzymes - organic cofactors (vitamins) –Inhibitors – substances that bind to enzyme and reduce its catalytic activity [cofactor] Reaction rate [inhibitor] Reaction rate

13. Factors Affecting Enzyme Activity Temperature –  Temp,  kinetic energy,  reaction rate –high Temp changes structure of enzymes  ’s enzyme function

14. Factors Affecting Enzyme Activity pH –3D structure of enzymes changes at different pH –optimal enzyme function at specific pH –  function at higher or lower pH’s

15. Metabolism –energetic sum of all chemical reactions occurring in a living organism –break down of some substances (catabolism) –build up of other substances (anabolism) Enzymes facilitate and control metabolism

16. Metabolism Metabolic Pathways –long series of enzyme-catalyzed reactions –allow high degree of control + regulation

17. How Does a Cell Maintain Order? Enzymes facilitate reactions, but cannot drive energetically unfavorable reactions –Unfavorable – would gain free energy as a result of the reaction To drive an energetically unfavorable reaction, it must be coupled to an energetically favorable one Cells require a supply of free energy (fuel) to drive biochemical reactions Reaction A: Gain free energy Reaction B: Lose free energy Reaction A + Reaction B = OVERALL LOSS OF FREE ENERGY!

18. Adenosine Triphosphate Energy carrier molecule ATP  ADP + P i + energy Energy used to drive biochemical reactions