1. Today:
Enzymes

3. What is a catalyst?

4. What is activation energy?

5. Enzymes lower activation energy (EA): how much energy needs to be put in the reaction to make it occur (destabilizes the bonds).

6. Enzymes DO NOT change ΔG
Enzymes DO NOT change ΔG. They cannot change the difference in energy levels between reactants and products!

7. We can lower the EA barrier with 2 things…. what are they?

8. Use in a sentence to explain what enzymes do: -substrate -active site -product

9. ENZYME-SUBSTRATE COMPLEX
ENZYME + PRODUCT(S)

11. Specificity- the enzyme only recognizes its specific substrate (even isomers are ignored!) Other factors affect specificity, such as optimum temperature & pH levels and induced fit.

12. The R- groups of the active site interact with the substrate and cause a conformational change in the enzyme. Makes it fit even more snugly with the substrate (induced fit).
Enzyme + substrate = enzyme-substrate complex.

13. Pepsin

14. EA lowers when 1) substrates are oriented correctly
EA lowers when 1) substrates are oriented correctly. This brings the substrate closer together. Closer = less distance over which the reaction has to occur = easier = lower EA.

15. Active sites lower EA when 2) the active site puts stress on the bonds that must be broken- makes it easier to separate molecules. (digestion)

16. Active sites lower EA 3) they produce a favorable microenvironment.

17. Active sites lower EA when 4) it participates directly in the reaction, which may include brief covalent bonds between the substrate and a R-group of the active site.

18. These things all help substrates reach their transition state more easily.

19. Environmental conditions can affect enzymes (pH, temperature, salinity, enzyme and substrate concentration, activators, inhibitors). More later.

20. Some enzymes get help. Cofactors- non-protein, small, inorganic compounds & ions that bind (Mg, K, Ca, Zn, Fe, Cu)
Fe in hemoglobin

21. Similar to cofactors are coenzymes, which are organic molecules that temporarily bind near the active site. Example: coenzyme A.

22. Some substances (inhibitors) inhibit enzymes
Some substances (inhibitors) inhibit enzymes. Many bind by weak interactions (reversible). If it forms a covalent bond, it’s irreversible inhibition (poisons, toxins).

23. Nerve gas sarin covalently binds to the R-group on serine in the active site of acetylcholinesterase.

24. Many antibiotics are inhibitors of specific enzymes in bacteria.

25. Competitive inhibitors bind to the active site (directly compete with substrate). Noncompetitive inhibitors bind to another part of the enzyme. Causes shape change and active site is less effective.

26. What kind of inhibition?

27. What kind of inhibition?

28. What kind of inhibition?

29. What is being shown here?

30. Allosteric regulation- conformational changes by regulatory molecules
Allosteric regulation- conformational changes by regulatory molecules. Allosteric inhibitors: keeps enzyme in inactive form. Allosteric activators: keeps enzyme in active form.

31. These molecules bind at the allosteric site of an enzyme (not all have this). This is not the same as the active site.

33. Some enzymes are made of multi subunits
Some enzymes are made of multi subunits. Another kind of allosteric activation for these types of molecules is cooperativity.

34. In cooperativity, when a substrate triggers induced fit in one subunit, it can trigger the same change in the other subunits (amplifies how responsive the enzyme is to other substrate molecules)
Hemoglobin- 4 subunits
Can bind 4 oxygens
1st oxygen binds; makes it easier for the other 3