Cell Energy Flashcards
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°C . 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.
Figure 1. The effect of pH on peroxidase activity
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?
Peroxidase activity will decrease.
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°C. 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.
Figure 1. The effect of pH on peroxidase activity
Which of the following actions will provide a negative control for the investigation?
Repeating the experiment using heat-denatured peroxidase
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°C. 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.
Figure 1. The effect of pH on peroxidase activity
One of the researchers proposes using oxygen gas production to measure reaction rates. Which of the following statements best justifies the use of the proposed modification as a way of creating an appropriate control for the investigation?
The experiment can be repeated without guaiacol, which will reveal the effect of guaiacol on the reaction rates.
Aminolevulinate dehydratase (ALAD) is an enzyme that relies on zinc as a cofactor. A zinc ion binds to the ALAD active site, where it forms favorable interactions with the side chains of three amino acids. Researchers have found that substituting a lead ion for a zinc ion in the ALAD active site causes inhibition of ALAD.
Which of the following statements best helps explain how the lead ion causes inhibition of ALAD?
It changes the three-dimensional structure of the active site so that ALAD is no longer compatible with its substrate.
Acetylcholinesterase (AChE) is a protein that catalyzes the conversion of acetylcholine to acetate and choline. When the concentration of AChE in an aqueous solution is held constant, the rate of the reaction catalyzed by AChE increases with increasing concentrations of substrate. At low concentrations of acetylcholine, a small increase in the substrate concentration results in a large increase in the reaction rate. At high concentrations of acetylcholine, however, a large increase in the substrate concentration results in only a small increase in the reaction rate.
Which of the following statements correctly explains the observed effect of the acetylcholine concentration on the rate of the enzyme-catalyzed reaction?
The active site of AChE is specific for acetylcholine, and only one substrate molecule can occupy the active site at a time.
A researcher proposes a model to explain how enzyme-substrate interactions determine enzyme specificity. The model is based on the idea that substrate molecules form favorable interactions with the amino acid side chains in an enzyme’s active site.
Based on the model, which of the following statements best explains an enzyme’s specificity for a particular substrate molecule?
A molecule with negative charges interacts with positively charged side chains in the enzyme’s active site.
Catalase is an enzyme found in yeast cells that facilitates the chemical breakdown of hydrogen peroxide to water and oxygen gas. An experiment was conducted to determine the effect of pH on catalase function. Five buffer solutions of varying pH (2, 4, 6, 8, and 10) were prepared and added to separate test tubes. Hydrogen peroxide (H2O2) was added to each test tube. Yeast was added, and the reactions were timed. After 1 minute the amount of oxygen gas released was determined by measuring the foam layer produced in each test tube. Figure 1 illustrates the experimental setup.
The figure illustrates the experimental procedure by showing 3 test tubes to indicate the sequence of steps. The first test tube contains a solution of a certain p H. H 2 O 2 is added to this tube. The second test tube contains the solution of a certain p H plus H 2 O 2. A yeast solution is added to this tube. After one minute, the third test tube shows a bracketed area above the surface of the solution, and the area is labeled Measure Foam Layer.
Figure 1. Illustration of experimental procedure
A set of five additional test tubes were prepared and used as controls. Which of the following best describes the contents expected to be contained in one of the five control test tubes?
pH 4 buffer solution and hydrogen peroxide only
A student designs an experiment to investigate the influence of temperature on enzyme function. The student’s plan is presented in Table 1.
Which test tubes are controls in the experiment?
Test tubes 1, 3, 5, and 7
A researcher designs an experiment to investigate whether soil bacteria trigger the synthesis of defense enzymes in plant roots. The design of the experiment is presented in Table 1. For each group in the experiment, the researcher will determine the average rate of change in the amount of defense enzymes in the roots of the seedlings.
Which of the following statements best helps justify the inclusion of group 2 as one of the controls in the experiment?
It will show whether the changes observed in group 1 depend on the metabolic activity of soil bacteria.
Pectinase is a protein that catalyzes the breakdown of pectic polysaccharides in plant cell walls. A researcher designs an experiment to investigate the effect of salinity on the ability of pectinase to lower the activation energy of the reaction involved. The design of the experiment is presented in Table 1. For each test tube, the researcher will measure the amount of product formed over 20 minutes.
Which of the following statements best helps justify the inclusion of test tube 5 in the experiment?
It will act as a control for test tube 6 by showing the effect of the presence or absence of the enzyme.
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?
Function will be disrupted by adding the urea and regained by removing the urea.
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.
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?
The amount of product will increase until the reaction reaches its equilibrium point or until the substrate is used up by the reaction.
European flycatchers feed caterpillars to their hatchlings. Graph 1 shows the average dates of hatching and fledging (leaving the nest), and the biomass of the caterpillars between early May (when flycatcher young hatch) and June (when fledging of young occurs).
Based on the data, scientists claim that the reproductive behavior of European flycatchers is influenced by the availability of energy sources. Which of the following statements best justifies this claim?
Young European flycatchers hatch from eggs when caterpillar biomass is available for the young birds to consume and convert into energy for growth.
A researcher claims that the incorporation of carbon dioxide into organic molecules during photosynthesis does not violate the second law of thermodynamics.
Which of the following statements best helps justify the researcher’s claim?
The total system that includes photosynthetic organisms and the Sun becomes less ordered over time.
Brown fat is a type of fat tissue found in hibernating mammals. Inside the mitochondria of these fat tissue cells, these mammals have an uncoupling protein embedded in the inner mitochondrial membrane. This uncoupling protein allows hydrogen ions to leak from the intermembrane space back into the mitochondrial matrix. Figure 1 shows details of the processes in the inner mitochondrial membrane.
Which of the following statements provides reasoning that supports the claim that brown fatty tissue keeps an animal warm?
The uncoupling protein in this tissue reduces the proton gradient across the membrane and thus produces heat to warm the animal without ATP production.
