1. Enzymes

2. Basic Features Speed up chemical reactions in your body
Made of protein
Act by lowering activation energy for reactions
“Lock and Key” method
Very specific (only do one reaction)
Can be reused!

3. Can be denatured (destroyed) by:
(a) Increasing Temperature (usually over 55C enzyme is destroyed)
(b) Changing pH out of optimum range
(c) Adding heavy metals (ex. Pb, Hg)

4. Enzyme Diagrams…
Ea = Activation Energy: Energy required to cause molecules to react with one another
Without Enzyme
A: Activation energy without an enzyme
B: Activation energy with an enzyme
C: Overall energy released during reaction
*An enzyme LOWERS the Ea!
Reactants
With Enzyme
Products

5. Substrate: Reactant(s) in an enzymatic reaction
Active site: Area of enzyme that binds with substrate
Enzyme: Acts as a CATALYST
Products: Freed and enzyme is available to be used again
“Lock and Key” Model  Each enzyme is SPECIFIC and fits its substrate PERFECTLY
Enzyme-Substrate Complex: When enzyme and substrate are bound

6. Types of Reactions
Degradative: substrate is broken into smaller pieces
Example- peptide  amino acids
Synthesis: substrates are joined to form larger molecules
Example- glucose  glycogen
Metabolic Pathway: Series of reactions that proceed in an orderly manner
- Each reactant is a substrate for a particular enzyme

7. Naming Enzymes Enzymes are often named for their substrate
Ex. SUBSTRATE ENZYME
Maltose Maltase
Ribonucleic Acid Ribonuclease

8. “Induced Fit” Model Differs from “Lock and Key”
Active site undergoes shape change to perfectly fit substrate
Once product(s) release, active site returns to original shape

9. Stopping Enzyme Activity
Feedback Inhibition
Competitive Inhibition
- Another molecule competes with true substrate for the active site
Non-Competitive Inhibition
- Another molecule binds to enzymes at a site other than the active site (called an ALLOSTERIC SITE)
- Changes 3D shape of the enzyme  can no longer bind to substrate

11. Feedback Inhibition (competitive or non competitive)
What’s happening?
End product is binding allosterically to Enzyme 1
This changes the active site shape  the pathway is SHUT DOWN

12. Enzyme Composition Made up of 2 parts: Apoenzyme (protein part)
Coenzyme OR Cofactor (non protein part)
Dietary Dietary
Organic Inorganic
Vitamins Metallic ions
Ex. K Ex. Ca2+

13. Example- Thyroxin Hormone produced by thyroid gland
Increases metabolic rate in cells
Increases # of respiratory enzymes in cells
Cause increase in O2 uptake

14. Graphing Enzyme Activity
We’ll discuss some common curves together for the following parameters:
Temperature pH
Substrate or enzyme concentrations

15. Temperature Activity increases due to increased kinetics
At a max temperature, enzyme starts to denature
Leads to rapid decrease in enzyme activity

16. pH Enzymes operate in a narrow pH range
As you move above or below this range, enzyme activity decreases due to denaturation
Ex. Enzyme pepsin works best at pH 2 (in the stomach)

17. Concentration Activity increases as substrate concentration increases
Due to greater likelihood of molecular collisions
Plateau  all active sites are occupied (enzyme is operating at capacity)