1. Enzymes
& Chemical Reactions

2. USES

3. But how do they work?

4. Background: Energy in Biochemical Rxns
Endothermic reactions: energy is absorbed
Product
Energy
Time
Energy stored
Reactant

5. Energy in Biochemical Rxns
Exothermic reactions: energy is released
What’s this?
Product
Energy
Time
Energy released
Reactant

6. Activation Energy Energy required to make or break chemical bonds.
Even exothermic reactions have activation energy.
Energy
Time
Activation energy

7. Enzymes Are protein catalysts.
Because they lower the amount of activation energy, they increase rate of reaction.
Are not consumed in reactions.
Cannot make reactions happen that wouldn’t happen normally.
Most enzymes can only work on 1 reactant

8. How?
Watch how the enzyme works:
Allosteric Site

9. The Catalytic Cycle! The substrate (reactant) enters the active site
The enzyme snuggles up to the substrate (called Induced Fit)
The enzyme-substrate complex bends (using energy) and breaks the substrate
The product is released and the enzyme prepares for the next substrate

10. Enzyme function
Enzyme may put two molecules together (Anabolic cycle):

11. Types of Enzymes
Kinase: Adds or removes phosphate groups, often from ATP
Hydrase (or hydrolase): Adds or removes water.
Isomerase: Changes the shape of molecules.
Oxidoreductase: Performs redox reactions.
Lyase: Breaks C-C bonds.
Ligase: Makes C-C bonds.

12. Factors Affecting Enzymes
pH and Temperature
Enzymes function best within a small range
Denaturation (unfolding of protein) occurs outside optimal range – protein no longer functions
Inhibitors
Certain molecules that can slow or stop enzyme function

13. Enzyme Inhibitors 2 Types:
Competitive: Inhibitor molecule has a similar shape to the substrate, so they compete for the active site: Slows enzyme
Non-competitive: Inhibitor fits into allosteric site & changes the shape of the active site: Stops enzyme
May not be permanent

14. Enzymes don’t always act alone!
Metabolic Pathway:
A series of enzymes that work together to form an end product.
The product of the 1st enzyme acts as the substrate for the 2nd enzyme…
Example: Photosynthesis: More than 10 enzymes work together in series to create sugar!

16. All together now… Feedback Inhibition:
A whole metabolic pathway can be inhibited by a single molecule!
Usually the end product acts as a noncompetitive inhibitor to the first enzyme in the pathway
Saves energy by limiting the amount of product