Chapter 13 (Enzyme kinetics) Flashcards
(15 cards)
What is the enzyme-substrate dissociation constant and its equation? How is it derived?
ks=k-1/k1
This equation is derived from the assumption that the rate of formation of ES and the rate of breakdown of ES are both happening in rapid equilibrium. Therefore:
k-1[ES]=k1[E][S]
and the expression can be found from there and the definition of ks.
Describe the difference in graphs of rate versus substrate concentration for allosteric and non allosteric enzymes.
non allosteric= hyperbolic. No small molecule effector needed.
allosteric= sigmoidal curve. Small effector molecule needed to relax enzyme conformation and allow binding to substrate.
Both exhibit first order characteristics at low [S] and zero order or saturation characteristics at high [S].
What is the equation for catalytic power and what does it signify?
Catalytic power=kcat/k
where kcat is the rate constant for the enzyme catalysed reaction.
Catalytic power shows the ratio of these and how much faster a reaction catalyzed by an enyme will proceed compared to a reaction not catalysed by an enzyme.
What do lyases do?
The add small molecules to a double bond or creat a double bond by eliminating small molecules.
apoenzyme versus a holoenzyme?
Apoenzyme is the inactive enzyme without its cofactor. A holoenzyme is the active form with the cofactor “prosthetic group attached to it.
What are the two reactions that Chymotrypsin can catalyze? Is this an allosteric or non allosteric enzyme?
1) hydrolysis of peptide bonds ( the connecting bond between amino acids) only on aromatic aa’s( trp, tyr, phe) and leu, gln, and lys.
2) hydrolysis of ester bonds.
Cymotrypsin is a non allosteric enzyme and will display a hyperbolic curve when velocity or rate of rxn is plotted against [S].
What type of enzymes can the Michaelis-Menten equation be applied to? What is the MM equation?
non allosteric enzymes.
v0=(vmax [S])/(km+[S])
What is km and what does it mean?
km is the measure of the affinity of an enzyme to its substrate. The lower the km, the higher affinity and stronger binding there is.
km=(k-1 +k2)/k1
ATcase is a what enzyme?
allosteric.
What two assumptions are made in the MM model and what do they mean?
1) Steady State Approximation
d[ES]/dt=0, [ES] quickly reaches a constant value.
2)Initial Velocity Approximation
NO reverse rxn from E+P=>ES is occurring
[P] initial=0
what is the equation for kcat and what does it mean
kcat=vmax/[Et}
This is the turnover number and tells how reactive the enzyme is. How many molecules it can take in and catalyze per second at every total active site.
What kind of inhibitors are there?
Reversible (non covalently bound) and irreversible (covalently bound)
What kind of reversible inhibitors are there?
Competitive, noncompetitive and uncompetitive.
What are the two kinds of competitive inhibition are there?
Classical, where the inhibitor blocks the active site by straight up attaching to it.
Non classical where the inhibitor binds to a different site, fucking up the active site so that the substrate cannot bind,
How are vmax and km affected in uncompetitive inhibition?
vmax and km both decrease. vmax because now there are EIS complexes and km because of le chatlier principle.
