Do Now 12/4

1. Do Now 12/4 • WOD: FRAY (fray) n. • fight or scuffle; brawl • The party turned into a FRAY when the bikers showed up. • A FRAY occurred in the cafeteria when Kirk spilled his lunch on Jody. • When Mark was beaned by the pitcher, a FRAY ensued between the teams. • Study for your Enzyme 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 on enzyme controlled reactions

2. Enzyme Inhibitors INB Pg 30

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 competitiveinhibitor 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 • http://www.youtube.com/watch?v=duN73LFWNlo

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 • http://www.youtube.com/watch?v=PILzvT3spCQ

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 inhibition P S E E S E E I I

14. Homework project – 10 pts • Using a sheet of computer paper and provided construction paper, design a poster that demonstrates: • Competitive inhibiton • 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 Friday @ end of class (will have time to work with partners in beginning)