1. Do Now 12/1 12 /1 Enzyme Inhibitors notes 22
Briefly sketch three graphs that show the initial reaction rates of enzyme catalyzed reactions with varying temperature, enzyme concentration, and substrate concentration. Label each graph, and compare the shape of each curve.

2. Enzyme Inhibitors
INB Pg 22

3. Inhibition Active site of enzyme fits perfectly to substrate
However, it is possible for another molecule to bind to an enzymes active site if it is very similar in shape to the enzyme’s substrate
This would inhibit the enzyme’s function
Substrate
Inhibitor
Enzyme

4. Competitive inhibition
A competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate.
The inhibitor competes for the same active site as the substrate molecule.

5. Competitive inhibitors
If a competitive inhibitor binds only briefly to the active site, there is competition between it and the substrate for the site
Which one “wins” depends on which has a higher concentration

6. Competitive inhibition
Usually reversible, because the inhibitor does not permanently bind to the enzyme
Inhibition can be reversed by increasing concentration of substrate

7. Competitive inhibition example
Methanol poisoning occurs because methanol is oxidized to formaldehyde and formic acid which attack the optic nerve causing blindness.
Ethanol is given as an antidote for methanol poisoning because ethanol competitively inhibits the oxidation of methanol.
Ethanol is oxidized in preference to methanol and consequently, the oxidation of methanol is slowed down so that the toxic by-products do not have a chance to accumulate.

8. Non-competitive inhibition
Inhibition does not depend on substrate concentration
Inhibitor will block enzyme function at low and high concentration of substrate
Two main types
Irreversible inhibition
Allosteric inhibition

9. Non-competitive irreversible inhibition
Sometimes, inhibitor can remain permanently bonded with the active site and therefore will cause an irreversible block to the substrate
No competition occurs because no matter how much substrate is present, the active sites will be permanently occupied by the inhibitor

10. Non-competitive irreversible inhibition
Penicillin works by permanently occupying the active site of an enzyme that is essential for the synthesis of bacterial cell walls
Penicillin and other β-lactam antibiotics act by inhibiting penicillin-binding proteins, which normally catalyze cross-linking of bacterial cell walls.

11. Non-competitive allosteric inhibition
If a molecule can bind to another site on the enzyme (besides active site) and stop enzyme function, it is an allosteric inhibitor
Can disrupt the 3D shape of enzyme molecule so active site cannot accept substrate
Can be reversible
or irreversible

12. End-product inhibition
As an enzyme converts substrate to product, it is slowed down because the end product binds to another part of the enzyme and slows down its function
Called negative feedback inhibition
The more product = slower reaction
Controls metabolic processes to stop enzyme from “running wild”

13. End product inhibitionS P E E S E E I I

14. Enzyme modeling– 10 pts
Using a sheet of computer paper and provided construction paper, design a poster that demonstrates:
Competitive inhibition
Irreversible non competitive inhibition
Allosteric inhibition
End-product (negative feedback) inhibition
Be sure to label the substrate, enzyme, and inhibitor!
On the back of each picture, briefly describe (1-2 sent.) the mechanism of inhibition
Due end of class (will have time to work with partners in beginning before quiz)

15. Chapter 3 quiz Concepts to know: lock and key hypothesis
Induced fit hypothesis
vocab: substrate, enzyme, active site, activation energy
reaction curves
effects of temperature, and pH, enzyme concentration, and substrate concentration on enzyme controlled reactions
Types of enzyme inhibition