Thermophiles are microorganisms that thrive at temperatures above 40 °C. Which of the following characteristics LEAST accurately describes an enzyme isolated from a thermophile?

Question

Thermophiles are microorganisms that thrive at temperatures above 40 °C.  Which of the following characteristics LEAST accurately describes an enzyme isolated from a thermophile?

Quizplus · Accepted Answer

11ecba2d_0ee9_a2f2_a3bf_3d05d8f9f41a_MD0008_00 Enzymes are macromolecules (usually proteins) that catalyze reactions by stabilizing the transition state-a high-energy molecule midway between substrate and product-within a pocket of the enzyme known as the active site. This stabilization requires the enzyme's active site to change shape upon substrate binding (seen in the induced fit model) to accommodate the shape of the transition state. The ability of the active site to adopt and maintain the correct shape is influenced by temperature. At low temperatures, molecular motion slows down and the active site becomes inflexible. Under these conditions the active site cannot easily change shape to accommodate the transition state, so the reaction rate is slow. At high temperatures, molecular motion speeds up and the intramolecular bonds that maintain the enzyme's tertiary structure are broken. This causes proteins to denature, destroying the shape of the enzyme's active site and halting catalytic activity. To facilitate survival, enzymes have evolved to operate at the environmental temperatures to which organisms are exposed. According to the question, thermophiles are microorganisms that thrive at temperatures above 40 °C. Therefore, enzymes from thermophiles typically have optimal activity above 40 °C and most likely have a relatively low catalytic rate at room temperature (25 °C) (Choices A and C). Thermophilic enzymes must be resistant to thermal denaturation so that they can maintain their tertiary structures at the high temperatures of their natural environment (Choice B). Although enzymes from thermophiles typically operate slowly below 37 °C, this is most likely due to inflexibility of the active site, not denaturation. Accordingly, thermophilic enzymes most likely maintain their tertiary structure below 37 °C because molecular motion at this temperature is too slow to break intramolecular bonds. Educational objective: Enzymes operate optimally at a temperature that is high enough for the enzyme to maintain flexibility but low enough that the enzyme does not denature. Most enzymes have evolved to operate optimally at the temperatures to which they are typically exposed in their host organisms.

Thermophiles Are Microorganisms That Thrive at Temperatures Above 40 °C