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Example Questions
Example Question #1 : Fundamentals Of Enzyme Kinetics
Why are the enzymes in lysosomes better and more active at an acidic pH than at a neutral pH?
It allows for regulation of their uptake by mitochondria
Since lysosomes are primarily found in the stomach acid of mammals, their pH dependence allows for maximum efficiency for the digestion of foodstuffs
It prevents them from accidentally degrading the macromolecules in the cytosol
It prevents their diffusion out of the lysosomes
It maximizes the interaction with their substrates, which are always bases
It prevents them from accidentally degrading the macromolecules in the cytosol
The hydrolytic enzymes found in lysosomes are pH-sensitive and function best in acidic environments. More specifically, when the pH of lysosomes change to an acidic pH of 4.8, the enzymes will become more active. These enzymes will not function well, or potentially at all, in alkaline (basic) environments. Since these enzymes have digestive capabilities, their pH activation helps to restrict their activity to the lumen of the lysosome.
Example Question #2 : Fundamentals Of Enzyme Kinetics
Why does a reaction acting at not increase in rate with the addition of more substrate?
A substrate at is saturated with enzyme
None of the other answers
An enzyme at is saturated with product
An substrate at is saturated with product
An enzyme at is saturated with substrate
An enzyme at is saturated with substrate
is the maximal velocity of an enzyme-catalyzed reaction. This occurs when all active sites of enzymes are occupied with substrate, and new openings will be filled immediately from the excess substrate. The enzyme is saturated with excessive substrate, so the reaction velocity no longer depends on substrate concentration.
Example Question #1 : Enzyme Kinetics And Models
What is the term for an enzyme that is noncovalently or covalently bound to a coenzyme?
Prosthetic enzyme
Holoenzyme
Apoenzyme
Kinase
Phosphorylase
Holoenzyme
Apoenzymes are holoenzymes without a coenzyme. There are no prosthetic enzymes, only prosthetic groups. Phosphorylases generally remove phosphate groups from substrates, and kinases generally add phosphate groups to substrates.
Example Question #1 : Enzyme Kinetics And Models
Which of the following terms describe the substrate concentration at which an enzyme's catalyzed reaction rate is at one-half of its maximum rate?
None of these
Michaelis constant
Rate constant
Equilibrium constant
Michaelis constant
From the answer choices, we see that there are a variety of constants that we're presented with. However, it is the Michaelis constant that signifies the amount of substrate at which an enzymatic reaction will be at half of its maximum value. The other constants, though related in some way to enzymatic reactions, do not answer the question.
The rate constant signifies the reaction rate at any given point in time, while the equilibrium constant is a thermodynamic value that tells us the spontaneity of the reaction.
Example Question #2 : Enzyme Kinetics And Models
Which of the following does not affect the velocity of an enzyme-catalyzed reaction?
pH
Enzyme concentration
Size of enzyme
Temperature
Substrate concentration
Size of enzyme
The size of an enzyme is typically not indicative of the rate of the reaction that it catalyzes. All other parameters are taken into account when considering reaction velocity.
Example Question #3 : Fundamentals Of Enzyme Kinetics
Which of the following describes first-order kinetics?
The rate of the reaction varies directly with the amount of reactant
The rate of the reaction varies with the square of the amount of reactant
The rate of the reaction is independent of the amount of reactant
The rate of the reaction varies with the square of the amount of product
The rate of the reaction varies directly with the amount of reactant
A first-order reaction is one in which the reaction rate varies directly with the concentration of the reactant. A zero-order reaction is one in which the reaction rate is independent of the concentration of the reactant. A second-order reaction is one in which the reaction rate varies directly with the square of the concentration of one reactant, or one in which the reaction rate varies directly with the concentration of two reactants.
Example Question #1 : Enzyme Kinetics And Models
Which of the following is true of allosteric enzymes?
Allosteric enzymes follow the same rules with respect to Michaelis-Menten kinetics that other enzymes do
Binding of one active site affects the binding of the other active sites
Allosteric enzymes do not have a
These enzymes only have one ligand binding site
Plotting reaction velocity against substrate concentration for an allosteric enzyme is linear
Binding of one active site affects the binding of the other active sites
Allosteric enzymes have multiple active sites, which affect each other. More often than not, allosteric enzymes will have sigmoidal plots when reaction velocity is plotted against enzyme concentration, and thereby display cooperativity. Cooperativity means that when one active site is bound by substrate, the other sites become easier to bind for substrate. Hemoglobin is a notable example of a protein that exhibits this type of enzyme kinetics.
Example Question #6 : Fundamentals Of Enzyme Kinetics
The oxygen binding curve for hemoglobin is sigmoidal, whereas that for myoglobin is hyperbolic. Why is this the case?
Both myoglobin and hemoglobin have four subunits, but myoglobin utilizes single-ligand binding whereas hemoglobin uses cooperative binding
Myoglobin, with one subunit, binds to a single ligand, whereas hemoglobin, with four subunits, utilizes cooperative binding
Hemoglobin, with one subunit, utilizes cooperative binding, whereas myoglobin, with four subunits, binds to a single ligand
Myoglobin, with four subunits, utilizes cooperative binding, whereas hemoglobin, with one subunit, binds to a single ligand
Myoglobin, with one subunit, utilizes cooperative binding, whereas hemoglobin, with four subunits, binds to a single ligand
Myoglobin, with one subunit, binds to a single ligand, whereas hemoglobin, with four subunits, utilizes cooperative binding
Both myoglobin (Mb) and hemoglobin (Hb) use heme groups to bind to oxygen. However, Hb contains four heme groups, whereas Mb contains only one. Single-ligand binding appears as a hyperbolic curve in ligand binding graphs, whereas sigmoidal curves indicate cooperative binding. As one ligand (oxygen) binds to hemoglobin, this makes it easier and more favorable for the second oxygen to bind, and so on for the third and finally the fourth oxygen; each oxygen binding allows the one following it to bind more easily. This behavior is responsible for creating the sigmoidal curve - the slope of the curve increases with pressure, indicating better binding capability, up to the point where the Hb starts to become totally saturated with oxygen molecules.
Example Question #1 : Fundamentals Of Enzyme Kinetics
Which of the following is not a method by which enzyme activity is regulated?
Covalent modification
Proteolytic cleavage
Kinetic control
Association with other peptides
Allosteric regulation
Kinetic control
Covalent modification - e.g phosphorylating a molecule to activate it.
Proteolytic cleavage - e.g zymogen becoming activated when cleaved.
Association with other polypeptides - e.g enzyme may have both catalytic and regulatory subunits - regulatory controls activity of the catalytic.
Allosteric regulation - e.g allosteric site on an enzyme that can become bound by a molecule, altering the protein's function.
Example Question #3 : Enzyme Kinetics And Models
Which of the following is false about enzymes?
They are substrate-specific
They change the equilibrium of product formation
None of these answers are false
They increase the rate of product formation
They lower the activation energy of product formation
They change the equilibrium of product formation
Enzymes are substrate specific molecules that lower the activation energy and increase the reaction rate of product formation. Enzymes do not change the equilibrium of product formation; this characteristic stays the same under the influence of enzymes.
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