In a simple chemical reaction, if you double the concentration of the reactants, what happens to the reaction rate?
The rate of an enzyme-catalyzed reaction only depends on the concentration of the enzyme. True or false?
FALSE. It depends on the concentration of the enzyme and substrate. The rate is determined by whichever of these is limiting. Normally this is the enzyme.
The maximum rate of the reaction.
At Vmax, what is happening with the active sites of the substrate?
Virtually all of them are filled with enzymes. I.e. the enzyme is all in the ES complex
The substrate concentration at which the reaction rate is half-maximal.
What will KM vary with?
temperature, pH, or the presence of inhibitors
The lower the KM....
The more likely an enzyme is to be operating at its Vmax
What would happen to Vmax and KM if we doubled the concentration of the enzyme?
Vmax would double KM would remain the same
Is competitive inhibition reversible? Non-competitive?
Competitive is always reversible, non-competitive sometimes is
Define competitive inhibition.
A molecule with a similar shape as the substrate complex is competing for access to the active site. However, when the inhibitor bonds it is not a productive reaction. It keeps the reaction from happening.
With a competitive inhibitor, an increase in substrate concentration when the inhibitor and enzyme concentrations are constant results in...
An increase in product. Higher substrate concentrations = higher reaction rate.
Does Vmax change with the presence of a competitive inhibitor? KM?
Vmax - no KM will be higher because it takes a higher substrate concentration to get the same rate of product formation
Define non-competitive inhibition.
The competitor binds to the enzyme but not the active site which somehow changes the shape of the active site.
Does Vmax change with the presence of a non-competitive inhibitor? KM?
Vmax lowers KM may or may not change
In the presence of a non-competitive inhibitor, does the substrate concentration affect the effectiveness of the inhibitor?
No. The degree of inhibition only depends on the concentrations of the inhibitor and enzyme.
How is inhibition measured?
Percent inhibition = (rate with inhibitor - rate without inhibitor)/(rate without inhibitor)
How do you determine if the inhibitor is competitive vs. noncompetitive?
Try a high concentration of substrate and a low concentration of substrate. No change in %inhibition = noncompetitive, lower concentration has a higher %inhibition = competitive
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