Lecture 12: Catalysis Flashcards
What do enzymes do?
lower activation energy
stabilize the transition state
What do enzymes not do?
change the delta G of reaction
irreversibly change shape
A catalyst is something that does what?
increase the rate of a reaction
but does not undergo any permanent chemical change as a result
What occurs when delta H is negative?
energy is released from the system
What occurs when delta H is positive?
energy is added to the system
What occurs when delta H is zero?
closed system
What occurs when delta S is negative?
disorder decreases
What occurs when delta S is positive?
disorder increases
What occurs when delta S is zero?
no net change in disorder
What occurs when delta G is negative?
free energy released; exergonic reaction; favorable reaction; spontaneous
What occurs when delta G is positive?
free energy required; endergonic reaction; unfavorable reaction; driven reaction
What occurs when delta G is zero?
equilibrium
What are two strategies to drive an unfavorable reaction?
- Maintain Q
What is the transition state?
a high energy, unstable form of the reactants that is ready to form a product
What is activation energy?
an energy barrier that must be overcome for the reaction to proceed
What ways can you speed up a reaction and overcome the activation energy barrier?
- raise temperature
2. stabilize the transition state (use an enzyme)
what is the induced fit model for substrate binding?
when a substrate binds, the enzyme changes shape so that the substrate is forced into the transition shape
Catalysis is achieved through:
substrate orientation
straining substrate bonds
creating a favorable microenvironment
covalent and/or non covalent interactions between enzyme and substrate
Describe covalent catalysis
enzyme covalently binds the transition state (electron transfer)
Describe acid base catalysis
partial proton transfer to the substrate
describe approximation
if electrons and/or protons are being exchanged, proper spatial orientation and close contact must occur and if they are right next to each other, the more they are able to react with one another (also called entropy reduction)
Describe electrostatic catalysis
stabilization of unfavorable charge on the transition state by polarizable side chains in the enzyme and/or metal ions
Serine proteases/ chymotrypsin problem faced (uncat)
reaction is too slow
Serine proteases/ chymotrypsin reaction substrates
polypeptide/peptide bond
Serine proteases/ chymotrypsin reaction products
shorter polypeptides
Serine proteases/ chymotrypsin type of enzyme
hydrolase
Serine proteases/ chymotrypsin type of reaction
hydrolysis
Serine proteases/ chymotrypsin reaction time (uncat)
years
Serine proteases/ chymotrypsin reaction time (cat)
milliseconds
Serine proteases/ chymotrypsin active site
catalytic triad + oxyanion hole
Serine proteases/ chymotrypsin specificity
hydrophobic specificity picket
Serine proteases/ chymotrypsin catalytic strategies
covalent catalysis
acid-base catalysis
carbonic anhydrases problem faced (uncat)
reaction is not fast enough
carbonic anhydrases reaction substates
CO2/HCO3-
carbonic anhydrases reaction products
HCO3-/CO2
carbonic anhydrases type of enzyme
hydrolase
carbonic anhydrases type of reaction
hydrolysis
carbonic anhydrases reaction time (uncat)
seconds
carbonic anhydrases reaction time (cat)
microseconds
carbonic anhydrases specificity
(size of entryway)
carbonic anhydrases catalytic strategies
acid base catalysis
approximation
electrostatic catalysis
Why do we need proteases?
recycling
regulation
defense
The active site of chymotrypsin is an example of _______
a catalytic triad
The ________ of chymotrypsin stabilizes the tetrahedral intermediate (transition state)
oxyanion hole
The _______ of chymotrypsin determines placement of cut
specificity pocket
