Question 1

Figure 6.3 Activity of various enzymes (a) at various temperatures and (b) at various pH.
-Which curves on the graphs in Figure 6.3 may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot spring at temperatures of 70°C or higher?
A) curves 1 and 5
B) curves 2 and 4
C) curves 2 and 5
D) curves 3 and 4
E) curves 3 and 5

Accepted Answer

The answer of  Figure 6.3 Activity of various enzymes...

Question 2

Alteration of an amino acid at a site distant from the active site of an enzyme may alter the substrate specificity of the enzyme by
A) changing the optimum pH for the enzyme.
B) changing the intracellular location of the enzyme.
C) changing the binding site for an allosteric regulator.
D) changing the conformation of the enzyme.

Accepted Answer

Altering the amino acid sequence of an enzyme can change its conformation and three-dimensional shape, which could affect the binding of substrates to the enzyme's active site. This change in the active site could also alter the substrate specificity of the enzyme, even if the altered amino acid is located far from the active site.

Question 3

Figure 6.1
-Which of the following is the most correct interpretation of Figure 6.1?
A) Inorganic phosphate is created from organic phosphate.
B) Energy from catabolism can be used directly for performing cellular work.
C) ADP + ℗i are a set of molecules that store energy for catabolism.
D) ATP is a molecule that acts as an intermediary to store energy for cellular work.
E) ℗i acts as a shuttle molecule to move energy from ATP to ADP.

Accepted Answer

Figure 6.1 shows the conversion of ADP to ATP and vice versa with the addition or loss of a phosphate group. ATP is a molecule that acts as an intermediary to store energy for cellular work. Therefore, D is the most correct interpretation. Options A, B, C, and E are incorrect interpretations of the figure.

Question 4

The mechanism by which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as
A) metabolic inhibition.
B) noncooperative inhibition.
C) irreversible inhibition.
D) feedback inhibition.

Accepted Answer

The mechanism described is feedback inhibition, where the end product of a metabolic pathway acts as an inhibitor of an earlier enzyme in the pathway. This is a form of negative feedback control of metabolism.

Question 5

In addition to regulating enzymes with activators and inhibitors, cells also regulate enzyme activity by
A) restricting enzymes to specific organelles or membranes.
B) limiting the availability of substrates.
C) covalently bonding enzymes into large aggregates.
D) secreting enzymes out of the cell.

Accepted Answer

The answer of In addition to regulating enzymes with activators...

Question 6

A severe fever can result in death if not brought under control because
A) it may destroy the primary structure of cellular enzymes.
B) it may alter the tertiary structure of cellular enzymes.
C) it may increase the rate of cellular chemical reactions.
D) it may result in binding inappropriate substrates by cellular enzymes.

Accepted Answer

A severe fever can cause the body temperature to rise significantly above the normal range, which can affect the tertiary structure of cellular enzymes. High temperature can cause the enzymes to denature, losing their shape, and thus becoming inactive, which can lead to a loss of chemical control in the body. This loss of control can result in the failure of vital organs leading to death.

Question 7

Under a particular set of conditions in the lab, the enzyme in a chemical reaction is saturated. Which of the following alterations to the reaction will increase the rate at which substrate is converted to product?
A) increasing the concentration of substrate in the reaction
B) increasing the amount of enzyme in the reaction
C) increasing the volume of the reaction without increasing the amount of substrate or enzyme
D) decreasing the concentration of product in the reaction

Accepted Answer

Increasing the amount of enzyme in the reaction will increase the rate of substrate conversion to product when the enzyme is saturated, as more enzyme molecules will be available to catalyze the reaction.

Question 8

Increasing the enzyme concentration in an enzymatic reaction could overcome which of the following?
A) denaturation of the enzyme
B) allosteric inhibition
C) competitive inhibition
D) saturation of the enzyme activity

Accepted Answer

Increasing the enzyme concentration can overcome saturation of the enzyme activity, as there will be more active sites available for the substrate to bind to and react with. However, increasing enzyme concentration will not overcome denaturation of the enzyme, allosteric inhibition, or competitive inhibition.

Question 9

An aminoacyl-tRNA synthetase is the enzyme that catalyzes the attachment of a particular amino acid to its corresponding tRNA. This reaction requires energy from ATP. The enzyme initially binds the amino acid and ATP, but it is unable to bind the tRNA. Which of the following would be a likely mechanism by which the enzyme ultimately binds the tRNA and attaches the amino acid?
A) Transfer of the ATP to the tRNA opens the active site to allow the tRNA to bind.
B) Hydrolysis of ATP activates the amino acid, which is released, opening up the active site to allow binding of the tRNA.
C) Hydrolysis of ATP phosphorylates the amino acid and results in a conformational change in the active site, which allows the tRNA to bind.
D) Alteration in the conformation of the tRNA allows it to bind to the active site along with the amino acid and ATP.

Accepted Answer

Hydrolysis of ATP phosphorylates the amino acid and results in a conformational change in the active site, which allows the tRNA to bind. This conformational change opens up the binding site for the tRNA to bind, forming a stable complex between the amino acid and the tRNA. The bound ATP is subsequently released and replaced by a molecule of inorganic phosphate (Pi). This process is repeated for each of the different amino acids that need to be added to the growing polypeptide chain during protein synthesis.

Question 10

Figure 6.3 Activity of various enzymes (a) at various temperatures and (b) at various pH.
-Which temperature and pH profile curves on the graphs in Figure 6.3 were most likely generated from analysis of an enzyme from a human stomach, where conditions are strongly acid?
A) curves 1 and 4
B) curves 1 and 5
C) curves 2 and 4
D) curves 2 and 5
E) curves 3 and 4

Accepted Answer

The enzyme from a human stomach is most likely to have a pH optimum in the acidic range, as the stomach environment is strongly acidic. Curves 1 and 4 show a pH optimum in the acidic range, so they are the most likely to have been generated from analysis of an enzyme from a human stomach.

Question 11

Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires mutations with amino acid changes that make them resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant viruses?
A) in or near the active site
B) at an allosteric site
C) at a cofactor binding site
D) in regions of the enzyme that determine packaging into the virus capsid

Accepted Answer

Amino acid changes that confer resistance to competitive inhibitors are most likely to occur in or near the active site of the reverse transcriptase enzyme, as this is where the inhibitor binds to the enzyme and prevents it from functioning.

Question 12

Cooperativity is a form of allosteric activation in which
A) the product of a metabolic pathway serves as a competitive inhibitor of an early enzyme in the pathway.
B) all of the enzymes in a metabolic pathway are contained within a single multienzyme complex.
C) completion of one step in a metabolic pathway is required before a subsequent step can occur.
D) binding of a substrate molecule to one active site in a multisubunit enzyme stimulates the binding of substrate molecules to the active sites of other subunits.

Accepted Answer

Cooperativity is a form of allosteric activation where binding of a substrate molecule to one active site in a multisubunit enzyme stimulates the binding of substrate molecules to the active sites of other subunits. This leads to a larger overall change in enzyme activity, resulting in more efficient catalysis.

Question 13

Which of the following is an example of cooperativity?
A) binding of an ATP molecule along with another substrate in an active site
B) binding of a molecule to one subunit of a tetramer, which promotes faster binding to each of the other three subunits
C) the product of one enzyme in a metabolic pathway serving as the substrate for the next enzyme in the pathway
D) binding of the end product of a metabolic pathway to the enzyme that catalyzes the first step in the pathway

Accepted Answer

Cooperativity occurs when the binding of a molecule to one subunit of a multimeric protein affects the binding of other subunits. In this case, the binding of a molecule to one subunit promotes faster binding to each of the other three subunits, demonstrating cooperativity. The other choices do not involve cooperativity.

Question 14

In experimental tests of enzyme evolution, a gene encoding an enzyme was subjected to multiple cycles of random mutagenesis and selection for altered substrate specificity. The resulting enzyme had altered substrate specificity and multiple amino acid changes. Where in the enzyme would you expect these amino acid changes to be located?
A) only in or near the active site
B) only in the hydrophobic interior of the folded protein
C) only at surface sites distant from the active site
D) in or near the active site and at surface sites distant from the active site

Accepted Answer

The alterations in substrate specificity and multiple amino acid changes suggest that mutations have occurred in or near the active site, which is responsible for the enzyme's catalytic activity. However, since the mutated enzyme was still functional and able to perform its job, it is likely that mutations have also occurred at surface sites that were distant from the active site. These changes may have altered the enzyme's overall structure and stability, allowing it to accommodate different substrates while maintaining its catalytic activity. Therefore, both the active site and surface sites distant from the active site could be affected by the evolution of new enzyme functions.

Question 15

Which of the following is true of enzymes?
A) Nonprotein cofactors alter the substrate specificity of enzymes.
B) Enzyme function is increased if the 3-D structure or conformation of an enzyme is altered.
C) Enzyme function is independent of physical and chemical environmental factors such as pH and temperature.
D) Enzymes increase the rate of chemical reaction by lowering activation energy barriers.
E) Enzymes increase the rate of chemical reaction by providing activation energy to the substrate.

Accepted Answer

Enzymes increase the rate of chemical reaction by lowering activation energy barriers. This is achieved by binding to the substrate and stabilizing the transition state, making it easier for the reaction to occur. Enzyme function is affected by physical and chemical environmental factors such as pH and temperature, and the 3-D structure or conformation of an enzyme is critical for its activity. Protein cofactors can aid in catalysis by enzymes, but nonprotein cofactors cannot alter substrate specificity.

Question 16

Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n)
A) competitive inhibitor of the enzyme.
B) noncompetitive inhibitor of the enzyme.
C) allosteric activator of the enzyme.
D) cofactor necessary for enzyme activity.
E) coenzyme derived from a vitamin.

Accepted Answer

Zinc is known to be a cofactor necessary for the activity of carboxypeptidase, as it is present in the active site and involved in catalysis. It is not a competitive or noncompetitive inhibitor, nor does it serve as an allosteric activator. Zinc is a metal ion, not a coenzyme derived from a vitamin.

Question 17

A noncompetitive inhibitor decreases the rate of an enzymatic reaction by
A) binding to the active site of the enzyme.
B) changing the ∆G for the reaction.
C) changing the shape of the enzyme active site.
D) decreasing the activation energy required for the reaction.

Accepted Answer

A noncompetitive inhibitor binds to a site on the enzyme that is not the active site, causing a conformational change in the enzyme that alters the shape of the active site. This makes it more difficult for the substrate to bind to the active site and decreases the rate of the enzymatic reaction. Noncompetitive inhibitors do not change the ∆G or activation energy of the reaction.

Question 18

Figure 6.2 Rate of an enzyme-catalyzed reaction as a function of varying reactant concentration, with the concentration of enzyme held constant.
-For the enzyme-catalyzed reaction shown in Figure 6.2, which of these treatments will cause the greatest increase in the rate of the reaction if the initial reactant concentration is 1.0 micromolar?
A) doubling the activation energy needed
B) cooling the reaction by 10°C
C) doubling the concentration of the reactants to 2.0 micromolar
D) doubling the enzyme concentration
E) increasing the concentration of reactants to 10.0 micromolar, while reducing the concentration of enzyme by half

Accepted Answer

The greatest increase in the rate of the reaction will occur by doubling the enzyme concentration (choice D), as this will increase the number of enzyme-substrate interactions and thus increase the rate of reaction. Increasing the concentration of reactants (choice C) will also increase the rate to some extent, but doubling the enzyme concentration will have a greater effect. Doubling the activation energy needed (choice A) or cooling the reaction by 10°C (choice B) will decrease the reaction rate. Increasing the concentration of reactants to 10.0 micromolar while reducing the concentration of enzyme by half (choice E) may have a similar effect on the rate as doubling the reactant concentration to 2.0 micromolar, but it will also reduce the number of enzyme-substrate interactions, resulting in a smaller overall increase in the rate.

Question 19

Figure 6.2 Rate of an enzyme-catalyzed reaction as a function of varying reactant concentration, with the concentration of enzyme held constant.
-In Figure 6.2, why does the reaction rate plateau at higher reactant concentrations?
A) Feedback inhibition by product occurs at high reactant concentrations.
B) Most enzyme molecules are occupied by substrate at high reactant concentrations.
C) The reaction nears equilibrium at high reactant concentrations.
D) The activation energy for the reaction increases with reactant concentration.
E) The rate of the reverse reaction increases with reactant concentration.

Accepted Answer

At high reactant concentrations, most enzyme molecules are already occupied by substrate. Therefore, increasing the substrate concentration further does not increase the rate of the reaction since there are not many free enzyme molecules left to bind with the additional substrate. This leads to a plateau in reaction rate.

Question 20

Figure 6.1
-Cells use the ATP cycle shown in Figure 6.1 to
A) recycle ADP and phosphate.
B) recycle energy released by ATP hydrolysis.
C) recycle the energy used for cellular work.
D) move energy from ATP to ADP.

Accepted Answer

Cells use the ATP cycle to recycle ADP and phosphate, which are the products of ATP hydrolysis, allowing them to be reused to form ATP again.

Quiz 6: An Introduction to Metabolism

Figure 6.3 Activity of various enzymes (a) at various temperatures and (b) at various pH. -Which curves on the graphs in Figure 6.3 may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot spring at temperatures of 70°C or higher?

Alteration of an amino acid at a site distant from the active site of an enzyme may alter the substrate specificity of the enzyme by

Figure 6.1 -Which of the following is the most correct interpretation of Figure 6.1?

The mechanism by which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as

In addition to regulating enzymes with activators and inhibitors, cells also regulate enzyme activity by

A severe fever can result in death if not brought under control because

Under a particular set of conditions in the lab, the enzyme in a chemical reaction is saturated. Which of the following alterations to the reaction will increase the rate at which substrate is converted to product?

Increasing the enzyme concentration in an enzymatic reaction could overcome which of the following?

Figure 6.3 Activity of various enzymes (a) at various temperatures and (b) at various pH. -Which temperature and pH profile curves on the graphs in Figure 6.3 were most likely generated from analysis of an enzyme from a human stomach, where conditions are strongly acid?

Cooperativity is a form of allosteric activation in which

Which of the following is an example of cooperativity?

Which of the following is true of enzymes?

Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n)

A noncompetitive inhibitor decreases the rate of an enzymatic reaction by

Figure 6.2 Rate of an enzyme-catalyzed reaction as a function of varying reactant concentration, with the concentration of enzyme held constant. -In Figure 6.2, why does the reaction rate plateau at higher reactant concentrations?

Figure 6.1 -Cells use the ATP cycle shown in Figure 6.1 to