Pepsin, an enzyme that hydrolyzes peptide bonds in proteins, functions in the stomach at a pH optimum of 1.5 to 2.0. How is the rate of a pepsin-catalyzed reaction affected by each of the following conditions?
c. running the reaction at 0 °C

Verified step by step guidance

1. Understand the role of temperature in enzyme activity: Enzymes, including pepsin, are proteins that catalyze reactions. Their activity is highly dependent on temperature. At lower temperatures, such as 0 °C, the kinetic energy of molecules decreases, leading to slower movement and fewer effective collisions between the enzyme and substrate.
2. Recall the concept of the optimal temperature for enzymes: Most enzymes have an optimal temperature range where their activity is maximized. For pepsin, this optimal temperature is typically around human body temperature (37 °C). Deviating significantly from this range, especially lowering the temperature, reduces the enzyme's catalytic efficiency.
3. Consider the effect of 0 °C on reaction rate: At 0 °C, the enzyme's activity is significantly reduced because the molecular motion is slowed down. This results in a lower rate of reaction, as fewer substrate molecules interact with the active site of pepsin.
4. Relate temperature to enzyme structure: While 0 °C does not denature pepsin (denaturation typically occurs at high temperatures), it does cause the enzyme to function less effectively due to reduced flexibility in its active site, which is necessary for binding substrates.
5. Conclude the impact: Running the reaction at 0 °C will slow down the rate of the pepsin-catalyzed reaction significantly, as the enzyme's activity is hindered by the low temperature.

Key Concepts

Enzyme Activity and Temperature

Enzymes, including pepsin, are proteins that catalyze biochemical reactions. Their activity is highly dependent on temperature; generally, as temperature increases, enzyme activity rises due to increased molecular movement. However, extreme temperatures can denature enzymes, leading to a loss of function. At low temperatures, such as 0 °C, enzyme activity is significantly reduced because molecular interactions slow down, resulting in fewer effective collisions between the enzyme and substrate.

pH and Enzyme Function

Enzymes have optimal pH ranges where they function most effectively. Pepsin, for instance, operates best in the highly acidic environment of the stomach (pH 1.5 to 2.0). Deviations from this optimal pH can lead to decreased enzyme activity or denaturation. At a neutral or basic pH, pepsin's structure may be altered, impairing its ability to hydrolyze peptide bonds efficiently.

Reaction Rate and Substrate Concentration

The rate of an enzyme-catalyzed reaction is influenced by substrate concentration. Initially, as substrate concentration increases, the reaction rate also increases, as more substrate molecules are available for the enzyme to act upon. However, this relationship only holds until the enzyme becomes saturated; beyond this point, additional substrate does not increase the reaction rate. At low temperatures, the reduced kinetic energy can further limit the effective concentration of substrate molecules interacting with the enzyme.