Lecture 12 Flashcards
What do enzymes do?
- Lower activation energy
- Stabilize transition state
What DONT enzymes do?
- change delta G of reaction
- irreversibly change shape
A catalyst is…
something that increases the rate/speed of a reaction but does not undergo any permanent chemical change as a result
What is the Induced Fit Model?
When a substrate binds in this model, the enzyme changes shape so that the substrate is forced into the transition state by:
- substrate orientation
- straining substrate bonds
- creating favorable microenvironment
- covalent and/or noncovalent interactions between substrate
Covalent Catalysis
transfer of electrons
Acid-Base Catalysis
Transfer of protons
Approximation
proximity and orientation
Electrostatic Catalysis
Noncovalent interactions
Chymotrypsin
An Active site that is an example of a catalytic triad
serine= nucleophile
histidine= base (proton acceptor)
aspartic acid= acid (proton donor)
oxyanion hole and specificity pocket
Oxyanion hold
built of serine and glycine, stabilizes the tetrahedral intermediate or transition state of chymotrypsin
Specificity Pocket
determines the placement of the cut in rxn
Carbonic Anhydrase
Active site contains Zn with 3 histidines and water
H2O facilitates trans state (deprotonated catalytic strategy of approximation)
has an Entry channel
Entry channel
determines the size of substrates used in Carbonic Anhydrase. CO2 is small and weakly polar for example.
What Biochemical strategies can be used to drive unfavorable reactions?
- maintain Q < K (create a pathway of products)
- couple rxn with a HIGHLY favorable reaction (ATP hydrolysis) Overall reactions and delta G values can be summed
