Enzyme Kinetics and Models

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Biochemistry › Enzyme Kinetics and Models

Questions 1 - 10
1

What does a small indicate?

That the enzyme requires only a small amount of substrate to become saturated

That the enzyme requires a large amount of substrate to become saturated

That high substrate concentrations are needed to achieve maximum reaction velocity

The enzyme has a low affinity for its substrate

Explanation

In enzyme kinetics, is the concentration of substrate which allows the enzyme to reach (maximum reaction velocity). A small indicates that only a small amount of substrate is needed for the enzyme to become saturated and thus for the reaction to reach maximum velocity. This also indicates that the enzyme and substrate have high affinity for one another. A large indicates that a large amount of substrate is needed for the enzyme to become saturated and thus for the reaction to reach maximum velocity.

2

What does a small indicate?

That the enzyme requires only a small amount of substrate to become saturated

That the enzyme requires a large amount of substrate to become saturated

That high substrate concentrations are needed to achieve maximum reaction velocity

The enzyme has a low affinity for its substrate

Explanation

In enzyme kinetics, is the concentration of substrate which allows the enzyme to reach (maximum reaction velocity). A small indicates that only a small amount of substrate is needed for the enzyme to become saturated and thus for the reaction to reach maximum velocity. This also indicates that the enzyme and substrate have high affinity for one another. A large indicates that a large amount of substrate is needed for the enzyme to become saturated and thus for the reaction to reach maximum velocity.

3

In a Lineweaver-Burk plot, the slope is                     .

Explanation

A Lineweaver-Burk is a double-reciprocal of the Michaelis-Menten equation. The equation for the graph, in form is:

From this graph, we can see that the slope is .

4

In a Lineweaver-Burk plot, the slope is                     .

Explanation

A Lineweaver-Burk is a double-reciprocal of the Michaelis-Menten equation. The equation for the graph, in form is:

From this graph, we can see that the slope is .

5

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

Size of enzyme

Substrate concentration

pH

Temperature

Enzyme concentration

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.

6

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

Size of enzyme

Substrate concentration

pH

Temperature

Enzyme concentration

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.

7

Which of the following is true of allosteric enzymes?

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

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

These enzymes only have one ligand binding site

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

Allosteric enzymes do not have a

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.

8

Which of the following is true of allosteric enzymes?

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

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

These enzymes only have one ligand binding site

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

Allosteric enzymes do not have a

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.

9

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

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

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

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

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

10

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

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

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

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

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

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