Biochem Chapter 6 Flashcards
Who discovered enzymes?
Edward Buchner
How do enzymes differ from ordinary chemical catalysts (4 ways)
- Can accelerate biochemical reactions faster
- Catalyze under mild conditions
- Give 100% yield
- Can be regulated
What kinds of bonds can an enzyme form with a substrate?
- Hydrophobic Effect
- Hydrogen Bond
- Ionic bond
- Covalent bond
Who developed the Lock and Key model of enzyme-substrate binding?
Emil Fischer
What are limitations of the lock and key model?
- Does not account for enzyme’s ability to bind diverse substrates
- Does not account for enzymes stabilizing transition state of rxn
Who developed the induced fit model?
Koshland
What is a cofactor?
Non-protein component
What is an apoenzyme?
Protein component (without cofactor)
What is a haloenzyme?
Apoenzyme + cofactor
What is a prosthetic group?
When the cofactor is tightly bound to the protein component
What 5 factors affect enzyme activity?
- Temp.
- pH
- Cofactors
- Allosteric Effectors
- Inhibitors
What are the 6 catalytic mechanisms for enzymes?
- Proximity Effects
- GABC
- Covalent (nucleophilic) catalysis
- Electrostatic stabilization
- Preferential stabilization of strained transition state
- metal ion catalysis
Describe Proximity effects
Positioning molecules close together for rxn
When you bring substrates close together for proximity effects, how is the significantly unfavorable loss in entropy paid for?
By the very favorable deltaH of enzyme + substrate binding
Describe GABC
Donating/Accepting a H+ by providing a weak acid/base group to stabilize an unstable TS & thus lower Ea
What groups can participate in GABC?
Tyr, Cys, Lys, Arg, His, Asp, Glu
Describe the roles of His 119 and His 12 in the RNase A Mechanism
Step 1: His 12 acts as a general base, abstracting a proton from 2’ hydroxyl of 3’ nucleotide ……. His 119 acts as a general acid, donating a proton to 5’ hydroxyl of nucleoside
Step 2: His 12 acts as a general acid, donating H+ to make ROH a good LG ……… His 119 acts as a general base, deprotonating H2O to make it a better nucleophile
What are the pKas of His 119 and His 12
His 119 = 6.4
His 12 = 5.4
Describe Covalent (nucleophilic catalysis)
Enzyme active site provides a nucleophile that forms a covalent Enz-S adduct that ALTERS THE REACTION PATHWAY (& thus lowers Ea)
What groups can undergo Covalent (nucleophilic) catalysis
Tyr, Cys, Lys, His, Asp, Glu, Ser, Thr
What is Lysine commonly used in the formation of?
Schiff bases/imines
What is the selectivity of Trypsin, Chymotrypsin, Elastase
Trypsin: Lys, Arg
Chymotrypsin: F, T, W
Elastase: Gly, Ala, Val, Ser
What catalytic mechanisms are involved the serine protease mechanism?
- GABC
- Covalent Catalysis
- Electrostatic Stabilization