🧬AP Biology
🧬AP Biology
FRQ 1 – Interpreting and Evaluating Experimental Results (Long)
Unit 1: Chemistry of Life
Practice FRQ 1 of 201/20
1. Enzymes are biological catalysts whose function depends heavily on their three-dimensional structure, which is determined by interactions between amino acids.
Researchers investigated the effect of temperature on the activity of alpha-amylase enzymes isolated from two different bacterial species: Escherichia coli, which lives in the human gut, and Geobacillus stearothermophilus, a thermophile found in hot springs. The researchers hypothesized that the enzyme from the thermophile would exhibit greater stability at higher temperatures due to specific structural adaptations.
To test this, the researchers incubated purified alpha-amylase from both species at temperatures ranging from 20°C to 90°C for 10 minutes. They then measured the enzyme activity by determining the rate of starch hydrolysis. The activity was normalized to the maximum activity observed for each enzyme, resulting in a value of Relative Enzyme Activity (%). A control reaction containing starch but no enzyme was included at each temperature to verify that starch hydrolysis was enzyme-catalyzed (Figure 1).
Structural analysis revealed that the alpha-amylase from G. stearothermophilus contains a salt bridge (an ionic interaction) between an arginine residue (Arg-120) and an aspartic acid residue (Asp-340) that is not present in the E. coli enzyme. To investigate the importance of this interaction, researchers created a mutant strain of G. stearothermophilus in which the aspartic acid at position 340 was replaced with alanine (Asp340Ala). They then measured the relative activity of the Wild-Type and Mutant enzymes at 75°C (Figure 2).
A. Describe how the properties of amino acid R-groups allow for the formation of a protein's tertiary structure.
Figure 1. Relative enzyme activity of alpha-amylase from E. coli and Geobacillus stearothermophilus after 10-minute incubation at temperatures from 20°C to 90°C. Activities are normalized to each enzyme’s own maximum activity (100%). Error bars show ±SEx. A no-enzyme control remains at 0% at all temperatures.
B.
i. Identify the dependent variable in the experiment shown in Figure 1.
ii. Justify the researchers' decision to include a control tube with no enzyme at each tested temperature.
iii. Based on Figure 1, describe the trend in enzyme activity for G. stearothermophilus as the temperature increases from 40°C to 75°C.
Figure 2. Relative enzyme activity at 75°C for G. stearothermophilus alpha-amylase: Wild-Type versus Asp340Ala Mutant. Activities are normalized so Wild-Type equals 100%. Error bars show ±SEx.
C.
i. Identify the independent variable in the experiment shown in Figure 2.
ii. Based on Figure 2, identify the effect of the Asp340Ala mutation on the activity of the enzyme.
iii. In a 5-minute trial at 75°C, the Wild-Type enzyme hydrolyzed 150 mg of starch, while the Mutant enzyme hydrolyzed 37.5 mg of starch. Calculate the difference in the rate of starch hydrolysis (in mg/min) between the Wild-Type and Mutant enzymes.
D.
i. The researchers claim that the salt bridge between Arg-120 and Asp-340 is critical for the thermostability of the enzyme. Using data from Figure 2, support the researchers' claim.
ii. Justify the claim that replacing aspartic acid with alanine would disrupt the salt bridge, based on the chemical properties of their R-groups.
