🧬AP Biology
1. Proteins are essential macromolecules that perform a diverse range of functions in biological systems, and their function is directly dependent on their specific three-dimensional structure.
Researchers isolated a novel enzyme, Enzyme Z, from a bacterium found in an acidic hot spring. To understand the factors affecting the enzyme's function, they compared the activity of the Wild Type Enzyme Z with a Mutant form that has a single amino acid substitution in its active site. The researchers incubated both enzymes at various pH levels ranging from 3 to 11 and measured the relative enzyme activity. The results are shown in Figure 1.
Following the pH experiments, the researchers investigated the stability of the enzymes in the presence of urea, a compound known to disrupt non-covalent bonds in proteins. They treated both the Wild Type and Mutant enzymes with 1.0 M urea and measured the remaining enzyme activity compared to untreated controls. The researchers hypothesized that the single amino acid substitution in the Mutant form alters its stability.
The researchers then conducted a second experiment to determine how the structural stability of the two enzyme variants is affected by a denaturing agent. They measured the enzyme activity of both the Wild Type and Mutant forms in the presence of 1.0 M urea and compared it to their activity in a control buffer without urea (Figure 2).
Describe the role of amino acid R-groups in the tertiary structure of a protein.
Figure 1. Effect of pH on the relative enzyme activity of Wild Type and Mutant Enzyme Z. Error bars show ±SE (5 percentage points).
Identify the dependent variable in the experiment shown in Figure 1.
Justify the researchers' decision to measure enzyme activity at pH levels both above and below pH 7.
Based on Figure 1, describe the trend in the activity of the Mutant enzyme as pH increases from 3 to 7.
Figure 2. Relative activity of Wild Type and Mutant Enzyme Z in the presence and absence of 1.0 M urea. Error bars show ±SE (5 percentage points).
Identify the independent variable in the experiment shown in Figure 2.
Based on Figure 2, identify the enzyme variant that demonstrates greater stability in the presence of urea.
The relative activity of 100% for the Wild Type Control corresponds to a reaction rate of 50 micromoles per minute. Calculate the reaction rate for the Wild Type enzyme in the presence of urea.
Researchers claim that the active site of the Mutant enzyme contains amino acids with different charge properties than the Wild Type. Using data from Figure 1, support the researchers' claim.
Researchers claim that the mutation results in the formation of an additional bond that stabilizes the tertiary structure of the protein. Justify this claim based on the data in Figure 2 and your understanding of protein structure.
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