1. Enzymes

2. Characteristics of Enzymes
Proteins
Catalysts
Speed up chemical reactions without being used up

3. How do enzymes work?
Lower Activation Energy to speed up rates of reaction
Reactions require energy to begin…enzymes lower the amount of energy required.

4. Naming Often end in “–ase”
The name usually relates to the reactants they are associated with or the reaction they help start
Examples: maltase, sucrase,
protease, carboxypeptidase

5. Catalyzing Process
A unique 3-D shape of an enzyme determines which chemical reaction it catalyzes
Important Vocab:
SUBSTRATE: A specific reactant that an enzyme acts on is called a substrate of the enzyme.

6. Important Vocab (cont.):
ACTIVE SITE: A substrate fits into a region of the enzyme called an active site.
An active site is typically a pocket or groove on the surface of the enzyme.

7. The enzyme and substrate form a complex
Active site
enzyme
Enzyme-substrate complex

8. Lock and Key Model
E S ES complex E P S P

10. Structure
If an enzyme’s shape is changed so that it is no longer able to catalyze reactions, we call it…
DENATURED
What kinds of things do you think could denature a protein?

11. Denaturation Disruption of protein structure by
Heat: Break apart H bonds and disrupt hydrophobic attractions
Acids/ bases: Break H bonds between polar R groups and ionic bonds
Heavy metal ions: React with S-S bonds to form solids
Agitation: Stretches chains until bonds break

12. Applications of Denaturation
Hard boiling an egg
Wiping skin with alcohol swab for injection
Cooking food to destroy E. coli
Heat used to cauterize blood vessels
Autoclave sterilizes instruments
Milk is heated to make yogurt

13. Think about it Solution
Tannic acid is used to form a scab on a burn. An egg becomes hard boiled when placed in hot water. What is similar about these two events?
Solution
Acid and heat cause a denaturation of protein. They both break bonds in the structure of protein.

14. Factors Affecting Enzyme Action
Temperature affects molecular motion
An enzyme’s optimal temperature produces the highest rate
Most human enzymes work best at ºC.
WATCH OUT!!!
If the temperature gets too high, the enzyme may be denatured!

15. Temperature (cont.) Optimum temperature Low High Reaction Rate

16. Ions: Salt concentration & pH influence enzyme activity.
SALT: The salt ions interfere with some of the chemical bonds that maintain protein structure
pH: The same is true of the extra hydrogen ions at very low pH
Optimal pH for most enzymes near neutral

17. Substrate Concentration
Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant) Why?
Maximum activity reached when all of enzyme combines with substrate

18. Substrate Concentration (cont.)
Maximum activity
Reaction
Rate
substrate concentration

19. Enzyme Inhibition Inhibitors: cause a loss of catalytic activity
May change the protein structure of an enzyme
May be competitive or noncompetitive
Some effects are irreversible

20. Competitive Inhibition
A competitive inhibitor
Has a structure similar to substrate
Occupies active site
“Competes” with substrate for active site
Effects can be reversed by increasing substrate concentration

21. Competitive Inhibition Image

22. Noncompetitive Inhibition
A noncompetitive inhibitor
Does not have a structure like substrate
Binds to the enzyme (not at active site) & changes the shape of enzyme & active site
Substrate cannot fit altered active site
No reaction occurs
Effect is not reversed by adding substrate

23. Noncompetitive Inhibition Image