Chapter 2: Enzymes Flashcards
What does endothermic mean?
A reaction that requires energy input
ΔH is positive
What does exothermic mean?
A reaction in which energy is given off.
ΔH is negative
How do enzymes affect the equilibrium of a reaction?
They do not affect the equilibrium.
They DO affect the rate of reaction
How do enzymes affect the rate of reaction?
The increase the rate of reaction by lowering the activation energy.
They make it easier for the substrate to reach the transition state.
What is a substrate?
The molecule upon which an enzyme acts
What is the enzyme active site?
The location within the enzyme where the substrate is held during the chemical reaction
What is the lock and key theory?
The enzyme’s active site (lock) is already in the appropriate confirmation for the substrate (key) to bind
No changes in tertiary or quarternary structure occur
What is the induced fit theory?
A substrate induces an appropriate conformational shift in the enzyme leading to the exposure of the active site. Following the reaction, the enzyme will return to its original shape
What is an apoenzyme?
Enzymes without their cofactors
What is a holoenzyme?
Enzymes with their cofactors
What is the major factor in reaction rate?
The concentration of the substrate [S] and enzyme [E] greatly affects how quickly a reaction will occur
Explain what enzyme saturation is
When substrate concentration is raised past a certain point, an enzyme has no available active sites for the excess substrate.
The enzyme is working at maximum velocity
The rate of reaction past the saturation point is independent of [S]
What is the [S] when the reaction rate equals 1/2 Vmax?
[S] = Km, the Michaelis Menten constant
What is the optimal pH of human blood?
7.4
Is a blood pH = 7.3 considerd acidosis or alkylosis?
Acidosis because the pH is lower than the normal blood level of 7.4
What is an allosteric enzyme?
An enzyme with multiple binding sites. One site is the active site, and another is a regulatory site that can affect the availability of the active site
Sigmoidal binding curve = Allosteric enzyme
What is competitive inhibition?
When an inhibitor can occupy the active site, thus preventing substrate binding. The substrate and inhibitor compete for access to the binding site.
This can be overcome by increasing [S]
What is noncompetitive inhibition?
When an inhibitor binds to an allosteric site instead of the active site. The two molecules do not compete, so increasing [S] will not overcome the inhibition
What is irriversible inhibition?
When the active site of an enzyme is made permanently unavailable or the enzyme is permanently altered.
What is a zymogen?
Inactive forms of enzymes that contain a catalytic and a regulatory domain. The regulatory domain is removed or altered in order to expose the active site.
