🧬AP Biology
1. Proteins are essential macromolecules that perform a diverse range of functions within living organisms, including catalyzing metabolic reactions.
Researchers are investigating the structural stability of Catecholase, an enzyme responsible for the browning reaction in fruits. The active site of the wild-type (WT) Catecholase enzyme contains a specific Aspartic Acid residue (a polar, negatively charged amino acid). The researchers created a mutant version of the enzyme (Mutant A) in which this Aspartic Acid residue was replaced by Alanine (a nonpolar, hydrophobic amino acid).
To determine how this mutation affects the enzyme's function under different environmental conditions, the researchers measured the relative activity of both the WT and Mutant A enzymes at pH 5, pH 7, and pH 9. The activity was calculated as a percentage relative to the maximum activity observed in the WT enzyme (Figure 1).
The researchers then investigated the thermal stability of the enzymes. They incubated samples of both the WT and Mutant A enzymes at five different temperatures (20°C, 30°C, 40°C, 50°C, and 60°C) for 10 minutes. After incubation, they cooled the samples to room temperature and measured the remaining enzyme activity (Figure 2).
Describe the chemical reaction that results in the formation of a peptide bond between two amino acids.
Figure 1. Average relative activity of Wild Type (WT) and Mutant A Catecholase enzymes at pH 5, pH 7, and pH 9. Activity is expressed as a percentage relative to the maximum activity observed for the WT enzyme (WT at pH 7 = 100%). Error bars show ±2SE.
Identify the dependent variable in the experiment shown in Figure 1.
Justify why the researchers included the measurement of the Wild Type enzyme at pH 7 in their experimental design.
Based on Figure 1, describe the effect of the mutation on the activity of the enzyme at pH 7 compared with the Wild Type.
Figure 2. Average relative activity of Wild Type (WT) and Mutant A Catecholase enzymes after incubation for 10 minutes at different temperatures. Error bars show ±2SE.
Identify the independent variable in the researchers' second experiment (data shown in Figure 2).
Based on Figure 2, identify the temperature at which the difference in activity between the Wild Type and Mutant A enzymes is the greatest.
The Catecholase enzyme consists of a single polypeptide chain containing 340 amino acids. Calculate the number of water molecules that were produced during the synthesis of this polypeptide chain.
Researchers claim that the mutation makes the enzyme less stable at higher temperatures. Using data from Figure 2, support the researchers' claim.
Justify the researchers' claim that replacing Aspartic Acid with Alanine affects the tertiary structure of the protein based on your understanding of the chemical properties of amino acid R-groups.
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