Question 1

The enzyme hexokinase catalyzes the reaction between ATP and glucose to form glucose 6-phosphate and ADP.In order to determine the efficiency of hexokinase, you wish to conduct an experiment to calculate its turnover number.To do so, you would set up

Accepted Answer

To calculate the turnover number of an enzyme, it is necessary to measure the rate of the enzyme-catalyzed reaction at saturating substrate concentrations. The reaction also requires ATP as one of the substrates. Therefore, option C is the best choice as it involves a reaction with a known amount of enzyme and saturating levels of glucose and ATP to calculate the turnover number. Option A does not provide substrate saturation, option B only uses glucose 6-phosphate, and options D and E involve varying conditions that may affect the rate of the reaction differently.

Question 2

Refer to the expression below. The enzyme alcohol dehydrogenase catalyzes this reaction in cells.The enzyme uses the coenzyme NAD⁺ in the reaction.Not shown are details about the active site, which contains a zinc ion that functions as a cofactor.How do the roles of cofactor and coenzyme compare in this particular case?

Accepted Answer

In this particular case, the cofactor (zinc ion) functions in the catalytic mechanism, changing only transiently, whereas the coenzyme NAD⁺ functions as a substrate and undergoes net chemical change as a result of the reaction catalyzed by alcohol dehydrogenase enzyme. Therefore, choice D is the best answer.

Question 3

In the presence of alcohol dehydrogenase, the rate of reduction of acetaldehyde to ethanol increases as the concentration of acetaldehyde increases.Eventually, the rate of the reaction reaches a maximum, at which point further increases in the concentration of acetaldehyde have no effect.Why?

Accepted Answer

This phenomenon is due to enzyme saturation. When all the active sites of the alcohol dehydrogenase molecules are occupied by acetaldehyde, the enzyme is working at its maximum capacity, and adding more substrate (acetaldehyde) cannot increase the rate of reaction further.

Question 4

Enzymatic reactions can become saturated as substrate concentration increases because

Accepted Answer

Enzymatic reactions can become saturated as substrate concentration increases because a limited number of enzyme molecules are present. At high substrate concentrations, all enzyme molecules may already be occupied by substrate and increasing the substrate concentration would not lead to an increase in the reaction rate. This is known as enzyme saturation. The other answer choices are not relevant to this phenomenon.

Question 5

Many enzymes require small nonprotein molecules for a reaction to occur.These molecules temporarily bind to and then are released from the substrate before participating in other reactions.These types of molecules are called

Accepted Answer

Coenzymes are nonprotein molecules that bind temporarily to an enzyme to assist in the reaction, and then are released to participate in other reactions.

Question 6

In order to determine whether a reaction is at "saturation," you can add _______ and determine whether the reaction rate _______.

Accepted Answer

Adding more substrate to a reaction will result in an initial increase in the reaction rate until the enzyme becomes saturated, meaning that all of the available enzyme active sites are bound to substrate molecules. At this point, the reaction rate will no longer increase with the addition of more substrate. Therefore, option B is the correct choice as it states adding more substrate to determine saturation.

Question 7

Which graph shows changes in the rate of an enzyme-catalyzed reaction as substrate concentration is varied?

Accepted Answer

Graph B shows a classic Michaelis-Menten curve, which describes changes in the rate of an enzyme-catalyzed reaction as substrate concentration is varied. The initial rate of the reaction increases as substrate concentration increases until it reaches a maximum velocity (Vmax) when all the enzyme active sites are saturated with substrate. At higher concentrations, the rate of the reaction plateau as there are no active sites left to bind substrate.

Question 8

You observe an enzymatic reaction that exhibits a standard relationship between reaction rate and substrate concentration as it converts substrate B to product C.When you add compound A, the creation of product C comes to a complete stop.You add large quantities of substrate B but still are unable to create product C in the presence of compound A.Compound A is therefore most likely a

Accepted Answer

Noncompetitive inhibitors bind to an enzyme at a site other than the active site, which can change the shape of the enzyme and prevent it from binding to its substrate. The fact that adding more substrate B does not overcome the inhibition suggests that compound A is not competing with substrate B for the active site, which is characteristic of noncompetitive inhibition.

Question 9

Refer to the figure below. NAD⁺ functions as a coenzyme in many enzyme-catalyzed reactions.The changes that take place in this coenzyme are the same for all of these reactions and are illustrated in the figure.It is likely that, in these reactions, NAD⁺

Accepted Answer

The answer of Refer to the figure below. NAD⁺...

Question 10

Competitive inhibitors of enzymes work by

Accepted Answer

Competitive inhibitors fit into the active site of an enzyme and compete with the substrate for binding. This prevents the substrate from binding and slows down the rate of the enzyme-catalyzed reaction.

Question 11

A noncompetitive inhibitor hinders binding of a substrate to an enzyme by

Accepted Answer

A noncompetitive inhibitor binds to a site on the enzyme (allosteric site) that is not the active site. This binding changes the shape of the enzyme's active site, making it unable to bind to the substrate effectively. This results in decreased enzyme activity and hindrance in binding of the substrate to the enzyme. Therefore, changing the shape of the active site is the correct choice.

Question 12

The addition of the competitive inhibitor mevinolin slows the reaction 
HMG-CoA$\rightarrow$ mevalonate, which is catalyzed by the enzyme HMG-CoA reductase.In order to overcome the effects of mevinolin and increase the rate of the reaction, you would

Accepted Answer

The addition of more substrate (HMG-CoA) would increase the likelihood of it binding to the active site of the enzyme, effectively outcompeting the inhibitor and increasing the rate of the reaction. Adding more of the product (mevalonate) would not overcome the effects of the inhibitor, as the inhibitor binds to the enzyme rather than the product. Lowering the temperature or rate constant would decrease the rate of the reaction, not increase it. Adding a prosthetic group may enhance the activity of the enzyme, but it would not directly overcome the effects of the inhibitor.

Question 13

How do competitive and noncompetitive enzyme inhibitors differ from each other?

Accepted Answer

Competitive inhibitors bind to the active site of the enzyme and compete with the substrate, whereas noncompetitive inhibitors bind to a different site on the enzyme and change its shape, making it unable to catalyze the reaction effectively.

Question 14

The inhibition of enzyme activity by noncompetitive inhibitors can be reduced

Accepted Answer

Noncompetitive inhibitors bind to an enzyme at a site other than the active site, which changes the shape of the enzyme and thus its activity. This inhibition cannot be overcome by changing substrate or inhibitor concentrations; it only ceases when the noncompetitive inhibitor dissociates from the enzyme.

Question 15

If you wanted to permanently block the function of an enzyme, you could add

Accepted Answer

Adding a molecule that covalently binds to the active site of the enzyme would permanently block the function of the enzyme by altering the shape of the active site and preventing the enzyme from binding to its substrate. Noncompetitive and allosteric inhibitors can be reversible and are not permanent solutions, while adding more product or competitive inhibitors would not permanently block the function of the enzyme.

Question 16

Which type of inhibitor can be overcome completely by the addition of more substrate?

Accepted Answer

Competitive inhibitors bind to the active site of the enzyme and prevent the substrate from binding. However, if more substrate is added, the chance of it binding with the active site increases, which can effectively overcome the inhibition. Noncompetitive inhibitors, on the other hand, bind to a different site on the enzyme and cannot be overcome by adding more substrate. Irreversible inhibitors permanently bind to the enzyme and cannot be overcome. Prosthetic inhibitors are not directly related to substrate binding and do not inhibit enzymes in the same way as competitive, noncompetitive, or irreversible inhibitors.

Question 17

You are working with an enzyme and wish to determine its saturation point.You note that the reaction rate increases slowly at first, then increases dramatically over a narrow range of substrate concentrations, and then levels off, creating a sigmoid reaction curve.It is likely that this enzyme is regulated by

Accepted Answer

The sigmoid reaction curve with a dramatic increase in reaction rate over a narrow range of substrate concentrations followed by leveling off indicates allosteric regulation. This means that the enzyme has a regulatory site, separate from the active site, that can bind to specific molecules and alter the enzyme's activity. This mode of regulation is not observed with temperature, pH, competitive inhibitors, or coenzymes.

Question 18

Which action would reverse the effects of a competitive inhibitor on an enzyme but not the effects of a noncompetitive or an irreversible inhibitor?

Accepted Answer

Adding substrate would increase the concentration of the substrate, making it more likely that it will bind to the active site of the enzyme instead of the competitive inhibitor. This would effectively reverse the effects of the competitive inhibitor. However, noncompetitive and irreversible inhibitors bind to sites on the enzyme other than the active site, so adding substrate would not affect their ability to inhibit the enzyme.

Question 19

An allosteric inhibitor

Accepted Answer

An allosteric inhibitor binds to a specific site on an enzyme, known as the allosteric site, which is different from the active site where the substrate binds. This binding causes a conformational change in the enzyme's shape, which decreases the enzyme's activity by either preventing substrate binding or hindering the catalytic activity of the enzyme. Therefore, choice B is the correct answer.

Question 20

Which statement about allosteric regulators is true?

Accepted Answer

Allosteric regulators often display a sigmoid curve in their plot of reaction rate versus substrate concentration, indicating a cooperative binding behavior between substrate molecules and regulatory molecules.

Answer: B
 Not all enzymes can be allosterically regulated. Only enzymes with multiple subunits or with certain functional domains are capable of being allosterically regulated.

Answer: C
 Allosteric regulators can affect both substrate binding and enzyme structure, leading to changes in catalytic activity.

Answer: D
 Allosteric regulators bind to specific sites on the enzyme, rather than nonspecifically.

Answer: E
 Allosteric regulators bind to specific sites on the enzyme, distinct from the active site, and can either enhance or inhibit enzyme activity.

Quiz 8: Energy, Enzymes, and Metabolism

The enzyme hexokinase catalyzes the reaction between ATP and glucose to form glucose 6-phosphate and ADP.In order to determine the efficiency of hexokinase, you wish to conduct an experiment to calculate its turnover number.To do so, you would set up

In the presence of alcohol dehydrogenase, the rate of reduction of acetaldehyde to ethanol increases as the concentration of acetaldehyde increases.Eventually, the rate of the reaction reaches a maximum, at which point further increases in the concentration of acetaldehyde have no effect.Why?

Enzymatic reactions can become saturated as substrate concentration increases because

Many enzymes require small nonprotein molecules for a reaction to occur.These molecules temporarily bind to and then are released from the substrate before participating in other reactions.These types of molecules are called

In order to determine whether a reaction is at "saturation," you can add _ and determine whether the reaction rate _.

Which graph shows changes in the rate of an enzyme-catalyzed reaction as substrate concentration is varied?

Refer to the figure below. NAD⁺ functions as a coenzyme in many enzyme-catalyzed reactions.The changes that take place in this coenzyme are the same for all of these reactions and are illustrated in the figure.It is likely that, in these reactions, NAD⁺

Competitive inhibitors of enzymes work by

A noncompetitive inhibitor hinders binding of a substrate to an enzyme by

The addition of the competitive inhibitor mevinolin slows the reaction HMG-CoA $\rightarrow$ mevalonate, which is catalyzed by the enzyme HMG-CoA reductase.In order to overcome the effects of mevinolin and increase the rate of the reaction, you would

How do competitive and noncompetitive enzyme inhibitors differ from each other?

The inhibition of enzyme activity by noncompetitive inhibitors can be reduced

If you wanted to permanently block the function of an enzyme, you could add

Which type of inhibitor can be overcome completely by the addition of more substrate?

Which action would reverse the effects of a competitive inhibitor on an enzyme but not the effects of a noncompetitive or an irreversible inhibitor?

An allosteric inhibitor

Which statement about allosteric regulators is true?

Quiz 8: Energy, Enzymes, and Metabolism

The enzyme hexokinase catalyzes the reaction between ATP and glucose to form glucose 6-phosphate and ADP.In order to determine the efficiency of hexokinase, you wish to conduct an experiment to calculate its turnover number.To do so, you would set up

In the presence of alcohol dehydrogenase, the rate of reduction of acetaldehyde to ethanol increases as the concentration of acetaldehyde increases.Eventually, the rate of the reaction reaches a maximum, at which point further increases in the concentration of acetaldehyde have no effect.Why?

Enzymatic reactions can become saturated as substrate concentration increases because

Many enzymes require small nonprotein molecules for a reaction to occur.These molecules temporarily bind to and then are released from the substrate before participating in other reactions.These types of molecules are called

In order to determine whether a reaction is at "saturation," you can add _______ and determine whether the reaction rate _______.

Which graph shows changes in the rate of an enzyme-catalyzed reaction as substrate concentration is varied?

Refer to the figure below. NAD+ functions as a coenzyme in many enzyme-catalyzed reactions.The changes that take place in this coenzyme are the same for all of these reactions and are illustrated in the figure.It is likely that, in these reactions, NAD+

Competitive inhibitors of enzymes work by

A noncompetitive inhibitor hinders binding of a substrate to an enzyme by

The addition of the competitive inhibitor mevinolin slows the reaction HMG-CoA →\rightarrow→ mevalonate, which is catalyzed by the enzyme HMG-CoA reductase.In order to overcome the effects of mevinolin and increase the rate of the reaction, you would

How do competitive and noncompetitive enzyme inhibitors differ from each other?

The inhibition of enzyme activity by noncompetitive inhibitors can be reduced

If you wanted to permanently block the function of an enzyme, you could add

Which type of inhibitor can be overcome completely by the addition of more substrate?

Which action would reverse the effects of a competitive inhibitor on an enzyme but not the effects of a noncompetitive or an irreversible inhibitor?

An allosteric inhibitor

Which statement about allosteric regulators is true?

In order to determine whether a reaction is at "saturation," you can add _ and determine whether the reaction rate _.

Refer to the figure below. NAD⁺ functions as a coenzyme in many enzyme-catalyzed reactions.The changes that take place in this coenzyme are the same for all of these reactions and are illustrated in the figure.It is likely that, in these reactions, NAD⁺

The addition of the competitive inhibitor mevinolin slows the reaction HMG-CoA $\rightarrow$ mevalonate, which is catalyzed by the enzyme HMG-CoA reductase.In order to overcome the effects of mevinolin and increase the rate of the reaction, you would