1. Enzyme Review Enzymes are…. Enzymes work by….
Environmental factors that effect enzyme activity are….

2. Enzymes are… Proteins Catalysts for biological reactions
something that speeds up a reaction. Up to 1012 fold
Usually end in ‘…ase’.
Name Identifies a reacting substance
sucrase – reacts sucrose
lipase - reacts lipid
Name describes function of enzyme
oxidase – catalyzes oxidation
hydrolase – catalyzes hydrolysis

3. Enzymes work by… Lowering the activation energy of a reaction.
Increasing the rate of reaction.

4. Mechanism for enzyme action: Lock and Key Model
A substrate(s) fits into a binding site on the enzyme called the active site.
The enzyme lowers the energy required to reach the transition state.
The product(s) is/are produced.

7. Enzyme Action: Induced Fit Model
Enzyme structure flexible, not rigid
Enzyme and active site adjust shape to bind substrate
Increases range of substrate specificity
Shape changes also improve catalysis during reaction

8. Enzyme Action: Induced Fit Model
E S ES complex E P P S S S P

10. Factors Affecting Enzyme Action
Optimum temperature
Reaction
Rate
Low High
Temperature
All enzymes have a temperature range within which they are most effective.
Denaturation

11. Factors Affecting Enzyme Action
Reaction
Rate
Optimum pH pH

12. Enzyme Activity & pH: Digestive enzymes

13. Factors Affecting Enzyme Action
Maximum activity
Reaction
Rate
substrate concentration
Enzyme cofactors
Vitamins
Phosphorylation
May affect concen-tration and enzyme action.

14. Enzyme Inhibition Inhibitors -Cause a loss of catalytic activity
-Change the protein structure of an enzyme
-May be competitive or noncompetitive
-Some effects are irreversible

15. Competitive Inhibition
A competitive inhibitor
Has a structure similar to substrate
Occupies active site
Competes with substrate for active site
Has effect reversed by increasing substrate concentration
Helps regulate the amount of product

16. Competitive Inhibition

17. Penicillin Mode of Action - Enzyme Inhibition:
All penicillin derivatives work by inhibiting proper bacterial cell wall synthesis.
If cell walls are improperly made cell walls allow water to flow into the cell causing it to burst.

18. Noncompetitive Inhibition
A noncompetitive inhibitor
Does not have a structure like substrate
Binds to the enzyme but not active site; called the allosteric site (allo = other, steric = space)
Changes the shape of enzyme and active site
Substrate cannot fit altered active site
No reaction occurs
Effect is not reversed by adding substrate

20. Competitive vs. Noncompetitive Inhibition

21. Enzyme Inhibition
May be irreversible: inhibitor permanently inactivates or destroys the enzyme.
EX: poisons
Cyanide is an inhibitor for the essential enzyme cytochrome c oxidase
Penicillin is poison to bacteria
Nerve gas inhibits acetylcholinesterase (necessary for proper nerve/muscle function).

22. And now a few thoughts about lab…
Liver = source of enzyme catalase
Hydrogen peroxide = substrate
Three different variables:
concentration
temperature pH

23. Catalase Protects Cells by Destroying Hydrogen Peroxide
2H2O H2O + O2
H2O2 is produced in the breakdown of fats and amino acids.
H2O2 is extraordinarily reactive and will damage the cell.
This occurs in an organelle called the peroxisome, which is also where catalase is found.
Catalase reduces the activation energy for the reduction of H fold
H2O2 is extraordinarily reactive and will damage the cell.