Enzymes Flashcards
What is the name of an active enzyme which has a bound cofactor?
holoenzyme
What is Km?
Km is an indicator of the affinity of the enzyme for its substrate. The higher the Km, the lower the affinity.
What is the influence of non-competitive inhibitors (reversible) on Km and Vmax?
The Km value does not change - still need the same amount of substrate to reach 1/2 Vo.
The Vmax decreases because the enzyme is being “removed” by the inhibitor. So, in effect, you have less enzyme available.
What does it mean when (S) = Km?
the rate of reaction is at half its maximal value
Define Km
the concentration of substrate required to produced half of the maximum velocity (Vmax) in a given reaction
How does free energy (delta G) relate to the spontaneity of a reaction?
a negative delta G is associated with a spontaneous reaction, with a lot of energy released.
How does the presence of an irreversible inhibitor effect Km and Vmax?
no effect on Km
Vmax will decrease
What is the difference between inducing and activating an enzyme?
inducing an enzyme means that you are increasing the genetic expression of an enzyme.
activating an enzyme causes an already existing enzyme to increase its output.
How does the presence of a noncompetitive (reversible) inhibitor affect Km and Vmax?
no effect on Km
Vmax will decrease
Can Km be altered by changing enzyme or substrate concentrations?
no
List the three classes of enzyme inhibitors.
competitive (reversible), non-competitive (reversible), and irreversible
What is delta G if a system is at equilibrium?
zero -> no net change can take place
How can we tell if a reaction will occur spontaneously?
if delta G is negative, the reaction is exergonic and therefore spontaneous
Enzyme A has a Km of 3 units for a certain reaction and enzyme B has a Km of 12 units for the same reaction. which enzyme has a greater affinity for the substrate is this reaction?
enzyme A
What is “activation energy”?
the difference in free energy between transition state and substrate. AKA Gibb’s free energy of activation.
If an enzyme has a very high Km, what does this mean?
the enzyme achieves a high rate of catalysis only at very high concentrations of substrate
What is an apoenzyme?
an enzyme that requires a cofactor to be active
how does the presence of a competitive (reversible) inhibitor affect Km and Vmax?
Km will increase
Vmax will stay the same
How does the presence of an irreversible (inactivator) inhibitor affect Km and Vmax?
no effect on Km
Vmax will decrease
Is Vmax affected by competitive inhibitors?
Vmax is unaffected because you retain the same amount of enzyme. the inhibitor can be overcome by higher substrate concentrations.
The free energy of activation describes the ___ of the reaction.
the rate of reaction (largely unrelated to the delta G of the reaction)
How does Km reflect the affinity between enzyme and substrate?
the lower the Km, the greater the affinity (enzyme for the substrate)
