🧬AP Biology
1. Enzymatic browning in damaged fruits is a chemical process catalyzed by the enzyme polyphenol oxidase (PPO). In the presence of oxygen, PPO converts phenolic compounds into dark-colored quinones.
PPO is a metalloenzyme that requires copper ions in its active site to function. Researchers investigated the effect of a copper-chelating agent, EDTA, on the activity of PPO extracted from Red Delicious apples. They hypothesized that removing copper ions would inhibit the enzyme's activity.
The researchers prepared PPO extracts and treated them with increasing concentrations of EDTA (0 mM, 5 mM, and 10 mM). They then measured the relative rate of quinone formation in each treatment group compared to the control (Figure 1).
The researchers then investigated a genetically modified 'Non-Browning' apple variety. They sequenced the PPO gene in both the Red Delicious and Non-Browning varieties and measured the total amount of quinone produced by extracts from each variety after 10 minutes (Figure 2).
Describe how the structure of an enzyme's active site contributes to its specificity for a substrate.
Figure 1. PPO activity in apple extracts
Identify the dependent variable in the experiment shown in Figure 1.
Justify why the researchers included the 0 mM EDTA treatment group in the experiment shown in Figure 1.
Based on Figure 1, describe the effect of increasing EDTA concentration on PPO activity.
Figure 2. Quinone production in apple varieties
Identify the independent variable in the researchers' second experiment (data shown in Figure 2).
Based on Figure 2, identify the apple variety that exhibits the lowest rate of enzymatic browning.
The PPO gene in Red Delicious apples contains 1,725 coding nucleotides. In the Non-Browning variety, a mutation results in a coding sequence of only 450 nucleotides. Assuming all nucleotides in the coding sequences encode amino acids, calculate the difference in the number of amino acids between the functional PPO protein and the mutant protein.
Researchers claim that the mutation in the Non-Browning variety renders the PPO enzyme non-functional. Using data from Figure 2, support the researchers' claim.
Justify the claim that the truncated protein sequence in the Non-Browning variety results in a loss of enzyme function based on your understanding of protein structure.
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