AP Biology : 3.3 Environmental Impacts on Enzyme Function - Exam Style questions with Answer- MCQ

AP PhysicsAP Calculus AP ChemistryAP Biology

Question

Researchers investigated the influence of environmental $pH$ on the activity of peroxidase, an enzyme that catalyzes the conversion of hydrogen peroxide to water and oxygen gas. In an experiment, the researchers added a hydrogen peroxide solution containing guaiacol to several identical test tubes and adjusted the solution in each test tube to a different $pH$ . The researchers included the guaiacol because it caused the solutions to change color as the reactions proceeded, which the researchers relied on for measuring reaction rates. Finally, the researchers added the same amount of peroxidase to each test tube and measured the rate of each reaction at $23 degrees Celsius$

. The results of the experiment are represented in Figure 1.

The figure presents a line graph in the coordinate plane. The horizontal axis is labeled p H, and the numbers 0 through 14, in increments of 2, are indicated. The vertical axis is labeled Relative Activity, and no numbers are indicated along it, although the axis ends in an arrowhead. The line begins at the point p H 0 with 0 relative activity, and moves horizontally to the right to p H 1 and 0 relative activity. The line then slants upwards and to the right at a constant rate until p H 2, then slants sharply upwards and to the right at a fairly constant rate until its peak at p H 5. The line then slants sharply downwards and to the right at a constant rate until p H 6, where the relative activity is half that of the peak. The line continues to slant sharply downwards and to the right at a constant rate until p H 7, where the relative activity is one tenth that of the peak. The line then slants less sharply downwards, and to the right at a constant rate until p H 9, where the relative activity is almost 0. The line then slants slightly downwards and to the right at an extremely low constant rate until p H 12 and p H 14, where relative activity drops to 0.

Based on Figure 1, which of the following statements best predicts the effect that a change from a moderately acidic environment (

pH

near 6) to a basic environment will have on peroxidase activity?

A. Peroxidase activity will decrease.

B. Peroxidase activity will increase.

C. Peroxidase activity will stay the same.

D. Peroxidase activity will increase at first and then decrease.

▶️Answer/Explanation

Ans: A
Based on Figure 1, peroxidase’s optimal $pH$ is 5. A change from a moderately acidic environment ( $pH$ near 6) to a basic environment ( $pH$ above 7) will result in a decrease in peroxidase activity.

Question

Researchers investigated the effect of urea on the three-dimensional structure of a certain enzyme. The researchers dissolved the enzyme in an aqueous buffer solution and added urea to the solution. The enzyme did not appear to have a secondary or tertiary structure. The researchers carefully removed the urea from the solution and determined that the enzyme had the original secondary and tertiary structure again.

Based on the results of the experiment, which of the following statements best predicts the effect of urea on the enzyme’s function?

A. Function will be disrupted by adding the urea and regained by removing the urea.

B. Function will be disrupted by adding the urea, but it will not be regained by removing the urea.

C. Function will be gained by adding the urea and disrupted by removing the urea.

D. Function will be unaffected by the addition and removal of the urea.

▶️Answer/Explanation

Ans: A
Based on the information, adding the urea denatures the enzyme, which will disrupt the enzyme’s function by disrupting the active site. In contrast, removing the urea causes the enzyme to refold, which will restore the active site and the enzyme’s function.

Question

In an experiment, a researcher prepares a reaction mixture by dissolving a substance in a buffered solution. The substance is the substrate of a certain enzyme. The researcher adds a small amount of the enzyme to the reaction mixture and measures the amount of product that is formed over time. The data are represented in Figure 1.

The figure presents the graph of a curve in the first quadrant of the coordinate plane. The horizontal axis is labeled Time, and no numbers are indicated along it. The vertical axis is labeled Amount of Product, and no numbers are indicated along it. Both axes end with arrowheads. The curve begins at the intersection of the 2 axes, then moves upwards and to the right at about a 45 degree angle. The curve then levels off, becoming approximately horizontal as it moves to the right. A point indicated about two thirds of the way along the horizontal region of the curve is labeled Add More Substrate.

Figure 1. The amount of product formed by an enzyme-catalyzed reaction over time

Which of the following best predicts the immediate result of adding more substrate to the reaction mixture at the point indicated by the arrow in Figure 1?

A. The amount of product will decrease until the reaction rate goes to zero.

B. The amount of product will decrease until the reaction reaches its equilibrium point or until the enzyme is been used up by the reaction.

C. The amount of product will increase until the reaction reaches its equilibrium point or until the substrate is used up by the reaction.

D. The amount of product will increase without stopping because the enzyme will be unchanged by the reaction.

▶️Answer/Explanation

Ans: C
The graph shown in Figure 1 indicates that the amount of product became constant as a consequence of the reaction reaching its equilibrium point or as a consequence of the substrate being used up. Adding more substrate will likely result in an increase in the amount of product because the reaction catalyzed by the enzyme will convert the added substrate into product.

Question

Alcohol dehydrogenase ( $ADH$ ) is an enzyme that aids in the decomposition of ethyl alcohol $(C_{2} H_{5} OH)$ into nontoxic substances. Methyl alcohol acts as a competitive inhibitor of ethyl alcohol by competing for the same active site on $ADH$ . When attached to $ADH$ , methyl alcohol is converted to formaldehyde, which is toxic in the body.
Which of the following statements best predicts the effect of increasing the concentration of substrate (ethyl alcohol), while keeping the concentration of the inhibitor (methyl alcohol) constant?

A. There will be an increase in formaldehyde because $ADH$ activity increases.
B. Competitive inhibition will be terminated because ethyl alcohol will bind to methyl alcohol and decrease $ADH$ activity.
C. The peptide bonds in the active site of the enzyme will be denatured, inhibiting the enzyme.
D. Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

▶️Answer/Explanation

Ans: D
The increase in amount of substrate will increase the number of enzyme-ethanol complexes formed, increasing the amount of nontoxic product formed from ethyl alcohol.

Question

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different $p H$ values was assessed by students in the lab. The students’ results are shown in graph 1.

Graph 1. Effect of $p H$ on peroxidase activity $p H$ $p H$

If the experiment is repeated at $pH$ 11, the observed activity level of the enzyme will most likely be

A. the same as the level at $p H$ 7
B. lower than the level at $p H$ 9
C. greater than the level at $p H$ 9
D. between the levels observed at $p H$ 5 and $p H$ 7.

▶️Answer/Explanation

Ans: B
Peroxidase activity drops off as the pH increases beyond 5, indicating that the optimal level was closer to $p H$ 5. The enzyme is likely to be further denatured by a $p H$ greater than 9. Since this enzyme occurs in many organisms, it is reasonable that the optimal $p H$ is closer to neutral than to a strongly basic or strongly acidic $p H$ .

AP Biology : 3.3 Environmental Impacts on Enzyme Function – Exam Style questions with Answer- MCQ

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