catalysis Flashcards
what do enzymes do
lower activation energy
stabilize the transition state
what do enzymes not do
change the deltaG of the rxn
irreversibly change shape
a catalyst is something that
increases the rate (speed) of a rxn
a catalyst does not
undergo any permanent chemical change as a result
induced fit model
when a substrate binds, the enzyme changes shape so that the substrate is forced into the transition state
(both enzyme and substate are distorted on binding)
catalysis is acheived through:
______ orientation
______ substrate bonds
______ a favorable microenvironment
______ and/or ______ interactions between enzyme and substrate
substrate
straining
creating
covalent and/or noncovalent
covalent catalysis
enzyme covalently binds the transition state (electrons transferred)
acid-base catalysis
partial proton transfer to the substrate
approximation catalysis
enzyme works to bring substrates into proper spatial orientation and close contact
approximation catalysis can also be called
entropy reduction
electrostatic catalysis
stabilization of unfavorable charges on the transition state by polarizable side chains in the enzyme and/or metal ions
serine proteases/chymotrysin and carbonic anhydrases are both what type of enzyme
hydrolases
active site for serine proteases/chymotrypsin
catalytic triad - serine (nucleophile), histidine (base-proton acceptor), aspartic acid (acid-proton donor)
oxyanion hole
specificity for chymotrypsin
hydrophobic specificity pocket
what catalytic strategies are used with chymotrypsin
covalent catalysis
acid-base catalysis
(approximation)
active site for carbonic anhydrases
3 histidines and Zn2+ OH-
specificity for carbonic anhydrases
size of entryway
what catalytic strategies are used with carbonic anhydrases
acid-base
electrostatic
approximation
why do we need proteases/chymotrypsin
recycling - degradation
regulation - removing proteins from circulation
defense mechanism - help chew up proteins
proteases are named for their
active sites
oxyanion hole in chymotrypsin functions to
stabilize the tetrahedral intermediate (transition state)
serine and glycine
what determines proper placement of cut with working with serine proteases such as chymotrypsin
specificity (S1) pocket
______ use carbonic anhydrases for carbon fixation
plants
carbonic anhydrases are important in humans for
pH regulation
carbonic anhydrase active sites contains
Zn++ ion
(Zn is coordinated to 3 histidines and a water)
(similar to MMPs)
carbonic anhydrases are an example of ______ evolution
convergent
in carbonic anhydrases, what facilitates the transition state
water
(lower pKa of water to just below physiological pH –> deprotonates water)
(definition of approximation)
specificity of carbonic anhydrases
very small and weakly polar molecules can get in active site
whats special about active site of carbonic anhydrase?
lowers pKa of water when it binds to Zn
approximation as substrate enters the active site
nucleophilic addition (adding CO2 to OH
release of product and regeneration of enzyme (histidine proton shuttle)
