Enzymes

1. Enzymes

2. Review of Reaction Terms • DG = (Free Energy of Products) - (Free Energy of Reactants)

3. Types of Reactions • Exergonic • Energy is released • DG is negative (more energy in reactants than products) • Spontaneous reaction

4. Types of Reactions • Endergonic • Absorbs energy (energy must be put into the reaction) • DG is positive (more energy in the products than the reactants) • Nonspontaneous reaction

5. Enzyme Function • Enzymes are proteins • Typically end in “ase” (ex. lactase) • Highly specific • Substrate = the molecules an enzyme acts on • Can be regulated • Return to original structure/shape after reaction • reusable

6. Enzyme Function • Immense catalytic power • Enzymes speed up a reaction by lowering the activation energy (EA) • Enzymes do NOT change the energy in the reactants or the products.

7. Enzyme-Substrate Complex substrates products Enzymes & Substrates • Enzymes bring substrates together in favorable ways in an Enzyme-Substrate Complex • Proximity and Orientation • Altered Environment (esp. a hydrophobic pocket) • Hydrogen Transfer • Move H from one molecule to another (to increase reactivity) • Enzyme binds the substrate in the active site

8. Active site Active Sites • Takes up relatively small part of enzyme • 3-D region that is put together by different parts of the linear structure • Clefts or crevices

9. Active Sites • Substrate bound to active site by: • Ionic attractions • Van der waals forces • Hydrophobic interactions • Hydrogen bonds

10. Induced Fit • Enzymes and substrates do not fit together like a lock and key • Active site is more flexible– molds around the substrate(s) • Like a glove around a hand

11. Inhibition • Competitive Inhibitor • Binds to the active site • Competes with the substrate • Can be overcome by adding more substrate • Noncompetitive Inhibitor • Binds to enzyme in an area other than the active site • Changes the shape of the active site to prevent substrate binding

12. Phosphate group Phosphorylation • Addition of a phosphate group to an enzyme • This changes its structure • Can either activate or inactivate the enzyme

13. Feedback Inhibition • Molecules can bind to enzymes at a “regulatory” site to inhibit its activity (like a noncompetitive inhibitor)

14. Allosteric Inhibition • When a protein’s function is affected by the binding of a molecule at a location other than the active site • Both allosteric inhibition and activation is possible.

15. Cooperativity • Occurs in enzymes with multiple subunits (chains) • Binding a substrate to one subunit makes it easier for all of the rest of the subunits to bind substrates

16. Other methods of Regulation • Some enzymes are synthesized in an inactive form and activated later by cleavage • Why would removing part of the enzyme changes its function? • Removing amino acids changes its structure which then changes its function

17. Effects of Temperature on Enzymes • Each enzyme has a particular temperature that it functions best at • At non-ideal temperatures: • Too high: Extra energy causes molecules to move around too much  bonds can’t be maintained • Too low: Active site becomes less flexible  can’t catalyze reactions as well.

18. Effect of pH on Enzymes • Each enzyme also has a pH that it functions best at • At non-ideal pHs excess H+ and OH- ions interfere with ionic attractions between + and – charged amino acids.