Intro to enzymes MCQ

Created by

Nisa

Cards (12)

A small molecule that decreases the activity of an enzyme by binding to a site other than the catalytic site is termed a(n)
Allosteric inhibitor
Enzymes are potent catalysts because they:
A)are consumed in the reactions they catalyse.
B)are very specific and can prevent the conversion of products back to substrates.
C)drive reactions to completion while other catalysts drive reactions to equilibrium.
D)increase the equilibrium constants for the reactions they catalyse.
E)lower the activation energy for the reactions they catalyse. 
E
Enzymes differ from other catalysts in that only enzymes:
A)are not consumed in the reaction.
B)display specificity toward a single reactant.
C)fail to influence the equilibrium point of the reaction.
D)form an activated complex with the reactants.
E)lower the activation energy of the reaction catalysed.
B
In competitive inhibition, an inhibitor:
A)binds at several different sites on an enzyme.
B)binds covalently to the enzyme.
C)binds only to the ES complex.
D)binds reversibly at the active site
D
One of the enzymes involved in glucose metabolism, aldolase, requires Zn 2+ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the:
A)apoenzyme
B)coenzyme
C)holoenzyme
D)prosthetic group
E)substrate
A
The concept of "induced fit" refers to the fact that:
A)enzyme specificity is induced by enzyme-substrate binding.
B)enzyme-substrate binding induces movement along the reaction coordinate to the transition state.
C)substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation.
D)when a substrate binds to an enzyme, the enzyme induces a loss of water from the substrate.
C
The role of an enzyme in an enzyme-catalysed reaction is to:
A)bind a transition state intermediate, such that it cannot be converted back to the substrate.
B)ensure that all of the substrate is converted to product.
C)ensure that the product is more stable than the substrate.
D)increase the rate at which substrate is converted into product.
E)make the free-energy change for the reaction more favourable
D
What is the definition of Km, the Michaelis constant?
A)The rate at which enzyme is turning substrate into product at 1/2 Vmax
B)The V0 at 1/2 maximal [S]
C)The number of molecules of substrate converted to product per second
D)The concentration of substrate at which the enzyme is operating at half its maximal velocity
E)The initial velocity (V0) of the enzyme when [S] << Km
D
Which of the following statements about a plot of V0 versus [S] for an enzyme that follows Michaelis-Menten kinetics is false?
A)As [S] increases, the initial velocity of reaction V0 also increases.
B)At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km.
C)Km is the [S] at which V0 = 1/2 Vmax.
D)The shape of the curve is a hyperbola.
E)The y-axis is a rate term with units of µM/min.
B
Which of the following statements is false?
A)After a reaction, the enzyme involved becomes available to catalyse the reaction again.
B)For S → P, a catalyst shifts the reaction equilibrium to the right.
C)Lowering the temperature of a reaction will lower the reaction rate.
D)The substrate binds to an enzyme's active site.
B
Which one of the following statements is true of enzyme catalysts?
A)Their catalytic activity is independent of pH.
B)They are generally equally active on D and L isomers of a given substrate.
C)They can increase the equilibrium constant for a given reaction by a thousandfold or more.
D)They can increase the reaction rate for a given reaction by a thousand-fold or more.
E)To be effective, they must be present at the same concentration as their substrate.
D
The following data were obtained in a study of an enzyme known to follow Michaelis Kinetics:
The Km for this enzyme is approximately:
A)1 mM
B)1,000 mM
C)2 mM
D)4 mM
E)6 mM
C