Biochemistry : Fundamentals of Enzyme Kinetics

Study concepts, example questions & explanations for Biochemistry

varsity tutors app store varsity tutors android store

Example Questions

← Previous 1

Example Question #1 : Enzyme Kinetics And Models

Why are the enzymes in lysosomes better and more active at an acidic pH than at a neutral pH?

Possible Answers:

It maximizes the interaction with their substrates, which are always bases

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 allows for regulation of their uptake by mitochondria

It prevents their diffusion out of the lysosomes

Correct answer:

It prevents them from accidentally degrading the macromolecules in the cytosol

Explanation:

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 : Enzyme Kinetics And Models

Why does a reaction acting at  not increase in rate with the addition of more substrate?

Possible Answers:

An enzyme at  is saturated with substrate

An substrate at  is saturated with product

An enzyme at  is saturated with product

None of the other answers

A substrate at  is saturated with enzyme

Correct answer:

An enzyme at  is saturated with substrate

Explanation:

 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 #3 : Enzyme Kinetics And Models

What is the term for an enzyme that is noncovalently or covalently bound to a coenzyme?

Possible Answers:

Kinase 

Phosphorylase

Apoenzyme

Holoenzyme

Prosthetic enzyme

Correct answer:

Holoenzyme

Explanation:

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 #4 : 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?

Possible Answers:

Michaelis constant

None of these

Equilibrium constant

Rate constant

Correct answer:

Michaelis constant

Explanation:

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 #1 : Fundamentals Of Enzyme Kinetics

Which of the following does not affect the velocity of an enzyme-catalyzed reaction?

Possible Answers:

pH

Temperature 

Size of enzyme

Enzyme concentration 

Substrate concentration

Correct answer:

Size of enzyme

Explanation:

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 #6 : Enzyme Kinetics And Models

Which of the following describes first-order kinetics?

Possible Answers:

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 with the square of the amount of reactant

The rate of the reaction varies directly with the amount of reactant

Correct answer:

The rate of the reaction varies directly with the amount of reactant

Explanation:

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 #2 : Fundamentals Of Enzyme Kinetics

Which of the following is true of allosteric enzymes?

Possible Answers:

Plotting reaction velocity against substrate concentration for an allosteric enzyme is linear

Allosteric enzymes do not have a 

Binding of one active site affects the binding of the other active sites

These enzymes only have one ligand binding site

Allosteric enzymes follow the same rules with respect to Michaelis-Menten kinetics that other enzymes do

Correct answer:

Binding of one active site affects the binding of the other active sites

Explanation:

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 #8 : Enzyme Kinetics And Models

The oxygen binding curve for hemoglobin is sigmoidal, whereas that for myoglobin is hyperbolic. Why is this the case?

Possible Answers:

Hemoglobin, with one subunit, utilizes cooperative binding, whereas myoglobin, 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

Myoglobin, with four subunits, utilizes cooperative binding, whereas hemoglobin, with one subunit, binds to a single ligand

Both myoglobin and hemoglobin have four subunits, but myoglobin utilizes single-ligand binding whereas hemoglobin uses cooperative binding

Myoglobin, with one subunit, utilizes cooperative binding, whereas hemoglobin, with four subunits, binds to a single ligand

Correct answer:

Myoglobin, with one subunit, binds to a single ligand, whereas hemoglobin, with four subunits, utilizes cooperative binding

Explanation:

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 #9 : Enzyme Kinetics And Models

Which of the following is not a method by which enzyme activity is regulated?

Possible Answers:

Association with other peptides

Kinetic control

Covalent modification

Proteolytic cleavage

Allosteric regulation

Correct answer:

Kinetic control

Explanation:

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 #10 : Enzyme Kinetics And Models

Which of the following is false about enzymes?

Possible Answers:

They change the equilibrium of product formation

They lower the activation energy of product formation

They increase the rate of product formation

They are substrate-specific

None of these answers are false

Correct answer:

They change the equilibrium of product formation

Explanation:

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. 

← Previous 1
Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: