1. Enzymes

2. What are enzymes?
Enzymes are proteins (tertiary and quaternary structures)
Act as a catalyst to accelerate reactions
Not permanently changed in the process

3. Enzymes Are specific for what they catalyze Are reusable End in –ase
Sucrase
Lactase
Maltase
Substrate
Enzyme
Active
site

4. How do enzymes work?
Enzymes weaken bonds, lowering the activation energy for the reaction
Enzyme lowers activation energy X
Free
energy
Reactants
Products
Reaction progress

5. How do enzymes work? Without enzyme With enzyme
Free energy of activation
Free
energy
Reactants
Products
Reaction progress

6. Enzyme-substrate complex
The substance (reactant) that an enzyme acts on is the substrate
Enzyme
Substrate

7. Induced fit
A change in the shape of an enzyme’s active site induced by the substrate
Substrate

8. Active site
A restricted region of an enzyme molecule which binds to the substrate is the active site
Enzyme
Active
site

9. Enzymes and reactions Enzyme without substrate (no reaction)
Enzyme + Substrate Products
H2O O2
(bubbles)
Liver
(Catalase enzyme)
Cubes
H2O2 +
Hydrogen peroxide
(Substrate)

10. Factors affecting enzyme activity
Temperature pH
Cofactors and coenzymes
Inhibitors

11. Temperature and pH
High temperatures are the most dangerous; they denature (unfold) enzymes
Most enzymes prefer temperatures near normal body temperature and near neutral pH
~ 37.5°C
pH of 6 to 8
Ionic salts also denature enzymes
Egg with denatured proteins

12. Cofactors and coenzymes
Inorganic substances (ie. zinc, iron) and vitamins are sometimes needed for proper enzymatic activity
Example:
Iron must be present in the
quaternary structure of
hemoglobin in order for it
to pick up oxygen

13. Enzyme inhibitors
Competitive inhibitors are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site
Enzyme
Substrate
Inhibitor

14. Enzyme inhibitors (Continued)
Noncompetitive inhibitors are chemicals that do not enter the active site
They bind to another part of the enzyme, changing the shape of the enzyme and altering the active site
Substrate
Inhibitor