Lecture 11: Enzymes II- Catalysis Flashcards
What do enzymes do?
- Lower activation rate
2. Stabilize the transition state
What DON’T enzymes do?
- Change the Delta G (Enthalpy/Free energy) of the reaction
2. Irreversibly change shape
Catalyst
Increases rate (speed) of a reaction, but does not undergo any permanent chemical change as a result
How do we speed up reaction/ overcome ACTIVATION BARRIER?
- Increased the energy of all molecules by increasing the temp (however proteins can be denatured)
- Lower the energy barrier by DECREASING the energy of the transition state**
Induced Fit Model
When substrate binds, the enzyme changes shape so that the substrate is forced into the transition state
How is catalysis achieved?
- Substrate orientation
- Straining substrate bonds
- Creating a favorable microenvironment
- Covalent and/or non-covalent interactions between enzyme and substrate
Catalysis Strategy #1- Covalent Catalysis
Enzyme covalently binds to the transition state (electrons transfer)
Catalysis Strategy #2- Acid-Base Catalysis
Partial proton transfer to the substrate
Catalysis Strategy #3- Approximation
For e/p’s to be exchanged, they must be in proper spatial orientation and close contact (proximity) for the reactant molecules must occur
–> If molecules held together in proper orientation, they are likely to interact = CALLED ENTROPY REDUCTION
If entropy (S) increases then
G (energy) increases always!
Catalysis Strategy #4- Electrostatic Catalysis
Stabilization of unfavorable changes on the transition state by polarizable side chains in the enzyme and/or metal ions
**Active site for Serine Proteases/Chymotrypsin
Catalytic triad and oxyanion hole
**Active site for Carbonic Anyhdrases
3 His + Zn++ - OH
**Specificity for Serine Proteases/Chymotrypsin
Hydrophobic specificity pocket
**Specificity for Carbonic Anhydrases
(Size of entryway)
