1. Lecture 4 Web: pollev.com/ucibio Text: To: 37607
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2. Lecture 4 objectives
Understand how active sites increase reaction rates
Understand the specificity of enyzmes
Know the structure and properties of amino acids
Know the functional groups and characteristics of amino acids

3. Enzymes and reactions Spontaneity = DG Rate = DG#
Enzyme = Decrease DG# = Increase rate
Mechanism = “Induced fit”
“Active site” weak interactions stabilize TS

4. Decreasing DG‡: Proximity + Orientation
Active site:
Bring products together
In precise orientation

5. Not just binding! Forces change in substrate conformation as well!
Keep molecules under “strain” to facilitate reaction
Active site interactions can stabilize the TS
Active site residues can initiate reactions
Different enzymes = Different mechanisms

6. Glc  Glc-6-P: Enzyme = Hexokinase

7. Specificity of enzymes - Isomers

8. Specificity of enzymes - Stereoisomers

9. Effects of specificity – Tastes!

10. Effects of specificity – Calories!

11. Effects of specificity – Treatment!

12. 3D shape is important!
OK. Fine. So the shape of the active site is important
How is the shape formed?

13. Formation of active sites

14. Active site review Small part of total enzyme
3D architecture is important
Specific residues important
Not necessarily contiguous residues

15. How does an active site form?
Protein must “fold”into structure
How does protein “fold?”
First, understand protein composition
Proteins made up of _____________

16. What is an amino acid?
Molecule with amino group and carboxylic acid group
H2N
COOH C R H
Each amino acid has a different “R” group
There are _____ different amino acids

17. Amino acids, pH and charge

18. Amino acid titration curve

19. Asp titration curve

20. Amino acids in cells…
H2N
COOH C R H

21. The Peptide bond: Joining amino acids

22. Nomenclature: Nt -> Ct

23. Charge on peptides is cumulative

24. OK. What does this all have to do with enzymes?
What is needed for proteins to fold correctly?
Can we design experiment to test?