MCAT® ExamBiological and Biochemical Foundations of Living SystemsHard
A scientist isolates a novel enzyme from a thermophilic bacterium. This enzyme exhibits optimal activity at 85°C and a pH of 7.5. If this enzyme were to be introduced into a human cell, which has a normal body temperature of 37°C and a cytoplasmic pH of approximately 7.2, what would be the most likely outcome regarding its activity?
- AIt would denature immediately due to the difference in pH.
- BIts activity would significantly increase due to the lower pH.
- CIts activity would be severely reduced due to suboptimal temperature.
- DIts activity would remain optimal because pH difference is minor.
Show answer & explanationAnswer & explanation
Correct answer: C. Its activity would be severely reduced due to suboptimal temperature.
Enzymes from thermophilic bacteria are adapted to high temperatures. A drop from 85°C to 37°C is a substantial deviation from its optimal temperature, leading to a severe reduction in activity, even if it doesn't immediately denature.
Why the other options are wrong
- A. While pH affects activity, a change from 7.5 to 7.2 is relatively small and generally not enough to cause immediate denaturation, especially compared to the extreme temperature shift.
- B. Lower pH (7.2 vs 7.5) is a minor change and unlikely to cause a significant increase; severe temperature change is more impactful.
- D. The temperature difference from 85°C to 37°C is far from minor and would drastically reduce activity, making the pH difference secondary.
Enzyme Activity Factors
Enzyme activity is highly sensitive to environmental conditions such as temperature, pH, and substrate concentration, which affect the enzyme's structure and catalytic efficiency.
- Optimal temperature maximizes kinetic energy for reactions without denaturation.
- Optimal pH maintains proper ionization states for active site residues.
- Deviations from optimal conditions can reduce activity or cause denaturation.
Memory trick: Enzymes are 'P'icky about 'T'emperature and 'P'H.