Enzymes and Metabolism

1. Enzymes and Metabolism Chapter 4

2. 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

3. 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… • Particular energetic properties of the reactant(s) vs. that of the product(s) • The concentration of the reactants(s) relative to that of the product(s)

4. 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]

5. 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.

6. 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

7. 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 Fig 4.1

8. 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 Fig 4.2

9. 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

10. Reaction Rate [E] 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 Fig 4.6

11. Reaction rate Reaction rate [cofactor] [inhibitor] 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 Fig 4.5

12. Factors Affecting Enzyme Activity • Temperature •  Temp,  kinetic energy,  reaction rate • high Temp changes structure of enzymes • ’s enzyme function Fig 4.3

13. 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 Fig 4.4

14. Metabolism • 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

15. Metabolism • Metabolic Pathways • long series of enzyme-catalyzed reactions • allow high degree of control + regulation Figs 4.7 & 4.8

16. 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!

17. Adenosine Triphosphate • Energy carrier molecule ATP  ADP + Pi + energy • Energy used to drive biochemical reactions Fig 4.15 & 4.16