Lecture 3: Enzyme Catalysis

Front 1

T/F catalysts alter the Keq of a reaction

Back 1

False
The keq of a reaction depends on the energy difference between the reactants and products. A catalyst does not change this difference but rather lowers the energy of activation required to overcome this distance

Front 2

What is the difference between kinetic and thermodynamic control

Back 2

kinetic control-the fastest product form is desiered, it may not be the most stable
thermodynamic-the most stable product is desired, it may not be the fastest formed but it will predominate at equilibrium

Front 3

Describe the unique 4 digit number used to classify enzymes

Back 3

1. one of six major classes
2 and 3. sub and sub sub class
4.accession number

Front 4

Describe the model of a non-catalyzed rxn in aqueous solution
How do the molecules come together? What makes them more likely to react?

Back 4

-the molecules must diffuse together, depends on temp and viscosity
-once together the molecules are caged by water molecules and collisions are frequent
-once in the encounter complex, the reactants must collidge with sufficient energy and in proper orientation for the rxn to occur
-note that during the collision the water molecules within the hydration spheres must be moved

Front 5

Explain how enzymes increase rxn rates using the proximity effect

Back 5

the enzyme brings the reactatns together insead of having to wait for them to diffuse and push water out of the way. these intermolecule rxns are much faster

Front 6

To be most effective, the catalytic site of an enzyme should be designed to fit which structure involved in the reaction

Back 6

Transition stae

Front 7

How does a hydrophobic microenvironment contribute to enzyme catalytic efficiency

Back 7

the hydrophobic environment exculdes solvent molecules and desolvates functional groups. This makes them siginificantly more reactive. This environments can also stabilize the transition state if it is less polar, which further reduces the energy of activation

Front 8

How do charged or polar amino acid side chains increase catalytic efficiency

Back 8

Charged or polar side chains near a reactive functional group can change the microenvironment and affect the pKa of the reactive group (see chymotripsin mechaism Asp)

Front 9

What is the difference between specific and general acid base catalysis

Back 9

specific-involves constituents of water H3O+ and OH-
general-involves weak acids such as amino acids

Front 10

Define Covalent catalysis

Back 10

results when a covalently bonded enzyme substrate intermediate is formed during the couse of the reaction (chymotrypsin rxn)

Front 11

Describe the role of each member of the catalytic triad of chymotripsin

Back 11

1. Ser-Oxygen in the R group acts as the nucelophile during the first attack on the peptide, it is later the leaving group when water attacks the remaining half
2. His-proton exchanger, accepts a proton during the initial peptide attack and later from water, unltimately gives it back to serine
3. Asp- polarizer, facilitates the positive charge on His by hydrogen bonding the oppositive proton

Front 12

Briefly describe the serine protease mechaism

Back 12

1. Serine O attacks the carbonyl carbon of the peptide
2. Tetrahedral group collapses and amine is leaving group (facilitated by His H bonding)
3. Water attacks the carbonyl group (again His H bonds)
4. Carboxcyclic acid is leaving group