[Campbell Biology P.207] Pepsin, a digestive enzyme, functions optimally at a very low pH ar... | Practice Question

Pepsin, a digestive enzyme, functions optimally at a very low pH around 2 . According to the text, why has natural selection likely favored this characteristic for pepsin, considering its location in the human body?

  • A: The low pH environment of the stomach would denature most other enzymes, but pepsin is evolutionarily adapted to maintain its structure and function in this acidic condition.
  • B: A low pH increases the reaction rate of all enzymes, so pepsin's optimal pH is simply a reflection of general enzyme kinetics.
  • C: Pepsin requires a low pH to bind to its substrate effectively, as its substrate is only stable under acidic conditions.
  • D: The acidic environment helps to activate pepsin from an inactive precursor, and this activation is pH-dependent.

Explanation

The text explicitly states: 'Such an acidic environment denatures most enzymes, but pepsin is well-adapted evolutionarily to maintain its functional 3-D structure in the acidic environment of the stomach.' This highlights that pepsin's low optimal pH is an evolutionary adaptation that allows it to function effectively in the harsh, acidic conditions of the stomach, where other enzymes would be rendered inactive.