Bio/Biochem Deck 2: Enzymes & Enzyme Kinetics
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33 Terms
What do enzymes do?
They speed up chemical reactions by lowering activation energy (Ea).
1) Do enzymes change ΔG?
2) Do enzymes change equilibrium?
No, They only lower activation energy and help equilibrium be reached faster.
What is the active site?
The region where the substrate binds and the reaction occurs.
What determines an enzyme's specificity?
The shape and chemical properties of its active site.
What is the lock-and-key model?
The active site already perfectly matches the substrate.
What is the induced-fit model?
The enzyme changes shape slightly when the substrate binds.
This is the model most enzymes follow.
What is Vmax?
The maximum reaction rate when every enzyme is saturated with substrate
What is Km?
The substrate concentration at which the reaction reaches ½ Vmax
What does a LOW Km indicate?
High affinity.
The enzyme binds substrate easily.
What does a HIGH Km indicate?
Low affinity.
More substrate is needed to reach ½ Vmax.
Which enzyme is more efficient: one with a Km of 2 μM or 20 μM?
The enzyme with Km = 2 μM because it has a higher affinity for its substrate.
What happens to reaction rate as substrate concentration increases?
The rate increases until the enzyme becomes saturated, then levels off at Vmax.
Where does a competitive inhibitor bind?
The active site.
Can increasing substrate concentration overcome competitive inhibition?
Yes.
The substrate can outcompete the inhibitor.
What happens to Km and Vmax during competitive inhibition?
Km increases → Apparent affinity decreases.
No change Vmax
Where does a noncompetitive inhibitor bind?
An allosteric site
Can increasing substrate overcome noncompetitive inhibition?
No
What happens to Km and Vmax during noncompetitive inhibition?
Km no change
Vmax decreases
When does an uncompetitive inhibitor bind?
Only after the substrate has already bound (enzyme-substrate complex)
What happens to Km and Vmax during uncompetitive inhibition?
Km decreases and Vmax decreases
Which inhibitor changes only Km?
Competitive
Which inhibitor changes only Vmax?
Noncompetitive
Which inhibitor changes both Km and Vmax?
Uncompetitive
What is an allosteric enzyme?
An enzyme regulated by molecules binding somewhere other than the active site
What is a positive allosteric regulator?
It increases enzyme activity
What is a negative allosteric regulator?
It decreases enzyme activity
What is feedback inhibition?
The final product of a pathway inhibits an earlier enzyme, preventing overproduction.
Why is feedback inhibition beneficial?
It conserves energy and resources.
What is the rate-limiting enzyme?
The slowest enzyme in a pathway that determines the overall reaction rate
Which glycolysis enzyme is rate-limiting?
Phosphofructokinase-1 (PFK-1).
What happens to enzyme activity as temperature increases?
Activity increases until the optimal temperature is reached.
Beyond that, activity drops due to denaturation.
How does pH affect enzymes?
Each enzyme has an optimal pH.
Extreme pH alters the active site's shape and decreases activity.
How do enzymes lower activation energy?
Properly orient substrates
Stabilize the transition state
Create a favorable microenvironment
Temporarily participate in the reaction