Question 1

-Consider the HIV enzyme called protease. The amino acid residues at the active site are highly hydrophobic. In designing a drug that would bind to the active site and jam it, researchers should use a molecule that is ________.
A) hydrophobic
B) polar
C) charged
D) acidic

Accepted Answer

Hydrophobic amino acid residues in the active site of the HIV protease would interact more favorably with a hydrophobic molecule, allowing it to bind effectively and inhibit the enzyme's function.

Question 2

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. 
-Which of the following represents the difference between the free-energy content of the reactants and the free-energy content of the products in the figure?
A) a
B) b
C) c
D) d
E) e

Accepted Answer

The answer of The following question(s) are based on the...

Question 3

Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's ________.
A) entropy
B) activation energy
C) endothermic level
D) equilibrium point
E) free-energy content

Accepted Answer

The activation energy is the energy required for the reactants to reach the transition state in a chemical reaction where they can form products. This is often the thermodynamic barrier that must be overcome for a reaction to occur. Therefore, B is the correct answer.

Question 4

A solution of starch at room temperature does NOT readily decompose to form a solution of simple sugars because ________.
A) the starch solution has less free energy than the sugar solution
B) the hydrolysis of starch to sugar is endergonic
C) the activation energy barrier for this reaction cannot easily be surmounted at room temperature
D) starch cannot be hydrolyzed in the presence of so much water
E) starch hydrolysis is nonspontaneous

Accepted Answer

The hydrolysis of starch into simple sugars is an exergonic process, but it requires an input of energy to overcome the activation barrier. Since the activation energy barrier cannot easily be surmounted at room temperature, starch does not readily decompose into simple sugars. Therefore, option C is the correct answer. Options A, B, D, and E are incorrect because they do not provide a valid explanation for the given phenomenon.

Question 5

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. 
-Which of the following represents the activation energy needed for the enzyme-catalyzed reverse reaction, C + D → A + B, in the figure?
A) a
B) b
C) c
D) d
E) e

Accepted Answer

The answer of The following question(s) are based on the...

Question 6

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) a competitive inhibitor of the enzyme
B) a noncompetitive inhibitor of the enzyme
C) an allosteric activator of the enzyme
D) a cofactor necessary for enzyme activity
E) a coenzyme derived from a vitamin

Accepted Answer

Zinc is a type of cofactor that is essential for the activity of carboxypeptidase. It acts as a catalytic site for the enzyme and is involved in binding and positioning substrates to facilitate their conversion. It is not an inhibitor or activator of the enzyme but is necessary for its function.

Question 7

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. -Which of the following terms best describes the forward reaction in the figure? A) endergonic, ∆G > 0 B) exergonic, ∆G < 0 C) endergonic, ∆G < 0 D) exergonic, ∆G > 0 E) chemical equilibrium, ∆G = 0

Accepted Answer

The forward reaction is exergonic, which means that it releases energy and has a negative value of ∆G. This can be inferred from the fact that the products (C and D) are at a lower energy level than the reactants (A and B) in the figure.

Question 8

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. 
-Which of the following in the figure would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?
A) a
B) b
C) c
D) d
E) e

Accepted Answer

The answer of The following question(s) are based on the...

Question 9

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

Accepted Answer

The answer of Which of the following is TRUE of...

Question 10

During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ∆G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the ∆G for the new reaction?
A) -40 kcal/mol
B) -20 kcal/mol
C) 0 kcal/mol
D) +20 kcal/mol
E) +40 kcal/mol

Accepted Answer

The ∆G for a reaction is independent of the amount of enzyme present in the reaction. Therefore, doubling the amount of enzyme in the reaction will not change the ∆G value. The ∆G for the new reaction will still be -20 kcal/mol.

Question 11

Rate of an enzyme-catalyzed reaction as a function of varying reactant
Concentration, with the concentration of enzyme constant.
In the accompanying figure, 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 of the enzyme molecules are occupied by substrate molecules, leading to a plateau in the reaction rate. This is because the enzyme molecules have reached their saturation point and cannot accommodate any more substrate molecules.

Question 12

-You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct?
A) The enzyme contains α-helices and β-pleated sheets.
B) The enzyme is subject to competitive inhibition and allosteric regulation.
C) Two types of allosteric regulation occur: The binding of one molecule activates the enzyme, while the binding of a different molecule inhibits it.
D) Either the enzyme has two distinct active sites or the reactants involved in the two reactions are very similar in size and shape.

Accepted Answer

Enzymes that catalyze two different chemical reactions either have two distinct active sites to accommodate different substrates or the substrates for the two reactions are very similar in size and shape, allowing them to fit into the same active site. This is a fundamental principle of enzyme specificity and catalysis.

Question 13

To attach a particular amino acid to the tRNA molecule that will transport it, an enzyme, an aminoacyl-tRNA synthetase, is required, along with ATP. Initially, the enzyme has an active site for ATP and another for the amino acid, but it is not able to attach the tRNA. What must occur for the final attachment to occur?
A) The ATP must first have to attach to the tRNA.
B) The binding of the first two molecules must cause a 3-D change that opens another active site on the enzyme.
C) The ATP must be hydrolyzed to allow the amino acid to bind to the synthetase.
D) The tRNA molecule must alter its shape to be able to fit into the active site with the other two molecules.
E) The 3' end of the tRNA must be cleaved before it can have an attached amino acid.

Accepted Answer

The binding of the ATP and the amino acid causes a conformational change in the enzyme that opens up a new active site, allowing the tRNA to bind and be attached to the amino acid.

Question 14

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 protein that determine packaging into the virus capsid
E) Such mutations could occur anywhere with equal probability.

Accepted Answer

Competitive inhibitors bind to the active site of the reverse transcriptase enzyme, blocking the enzyme's activity. Mutations that change amino acids in or near the active site could alter the shape of the active site, making it less able to bind to the inhibitor, thus leading to drug resistance.

Question 15

Which of the following statements is TRUE about enzyme-catalyzed reactions?
A) The reaction is faster than the same reaction in the absence of the enzyme.
B) The free-energy change of the reaction is opposite from the reaction that occurs in the absence of the enzyme.
C) An enzyme catalyzes a reaction by raising the activation energy.
D) Enzyme-catalyzed reactions require energy to activate the enzyme.
E) Enzyme-catalyzed reactions release more free energy than noncatalyzed reactions.

Accepted Answer

Enzyme-catalyzed reactions are faster than the same reaction in the absence of the enzyme. This is because enzymes lower the activation energy required for the reaction to occur, allowing the reaction to proceed more quickly.

Question 16

Enzymes ________.
A) increase the rate of a reaction by making the reaction more exergonic
B) increase the rate of a reaction by lowering the activation energy barrier
C) increase the rate of a reaction by reducing the rate of reverse reactions
D) change the equilibrium point of the reactions they catalyze
E) make the rate of a reaction independent of substrate concentrations

Accepted Answer

Enzymes lower the activation energy barrier, which enables the substrate to reach the transition state more easily and hence increase the rate of the reaction. This allows the reaction to occur more quickly and efficiently than it would without the enzyme present.

Question 17

The active site of an enzyme is the region that ________.
A) binds allosteric regulators of the enzyme
B) is involved in the catalytic reaction of the enzyme
C) binds noncompetitive inhibitors of the enzyme
D) is inhibited by the presence of a coenzyme or a cofactor

Accepted Answer

The active site of an enzyme is the region that is involved in the catalytic reaction of the enzyme. It is where the substrate binds and is transformed into the product. The other options are incorrect because allosteric regulators, noncompetitive inhibitors, coenzymes, and cofactors may bind to other regions of the enzyme and affect its activity, but not necessarily the active site.

Question 18

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. 
-Which of the following represents the ΔG of the reaction in the figure?
A) a
B) b
C) c
D) d
E) e

Accepted Answer

The answer of The following question(s) are based on the...

Question 19

The lock-and-key analogy for enzymes applies to the specificity of enzymes ________.
A) as they form their tertiary structure
B) as they form their tertiary and quaternary structure
C) binding to their substrate
D) interacting with water
E) interacting with ions

Accepted Answer

The lock-and-key analogy for enzymes applies to the specificity of enzymes binding to their substrate. Just as a key fits specifically into a lock, a substrate molecule fits specifically into the active site of an enzyme. This specificity is crucial for the catalytic activity of enzymes.

Question 20

According to the induced fit hypothesis of enzyme catalysis, ________.
A) the binding of the substrate depends on the shape of the active site
B) some enzymes change their structure when activators bind to the enzyme
C) a competitive inhibitor can outcompete the substrate for the active site
D) the binding of the substrate changes the shape of the enzyme's active site
E) the active site creates a microenvironment ideal for the reaction

Accepted Answer

According to the induced fit hypothesis, the substrate binding to the enzyme's active site leads to a conformational change in the enzyme, resulting in a better fit between the two. This change in shape of the enzyme's active site enhances the catalytic ability of the enzyme.

Quiz 8: Energy and Enzymes: an Introduction to Metabolism

-Consider the HIV enzyme called protease. The amino acid residues at the active site are highly hydrophobic. In designing a drug that would bind to the active site and jam it, researchers should use a molecule that is ________.

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. -Which of the following represents the difference between the free-energy content of the reactants and the free-energy content of the products in the figure?

Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's ________.

A solution of starch at room temperature does NOT readily decompose to form a solution of simple sugars because ________.

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. -Which of the following represents the activation energy needed for the enzyme-catalyzed reverse reaction, C + D → A + B, in the figure?

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

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. -Which of the following terms best describes the forward reaction in the figure?

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. -Which of the following in the figure would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?

Which of the following is TRUE of enzymes?

During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ∆G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the ∆G for the new reaction?

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

-You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct?

Which of the following statements is TRUE about enzyme-catalyzed reactions?

Enzymes ________.

The active site of an enzyme is the region that ________.

The following question(s) are based on the reaction A + B ↔ C + D shown in the accompanying figure. -Which of the following represents the ΔG of the reaction in the figure?

The lock-and-key analogy for enzymes applies to the specificity of enzymes ________.

According to the induced fit hypothesis of enzyme catalysis, ________.