Problem Set: Applying Enzyme Knowledge to Data
Problem 1: pH-Activity Curve Interpretation
A student measures the activity of two digestive enzymes at different pH values and plots the results:
- Enzyme X: maximum activity at pH 6.8; activity drops sharply below pH 4.0 and above pH 8.0
- Enzyme Y: maximum activity at pH 1.7; activity negligible above pH 4.0
Questions:
Q1.1: Identify Enzyme X and Enzyme Y.
- Answer: Enzyme X = Salivary amylase (optimal pH 6.8). Enzyme Y = Pepsin (optimal pH 1.5–2.0). The sharp drop below pH 4 for Enzyme X matches salivary amylase being destroyed by stomach acid.
Q1.2: If a person swallows a food bolus containing starch, at which point does Enzyme X stop working?
- Answer: Enzyme X (salivary amylase) stops working when the bolus reaches the stomach (pH 1.5–2.0). The stomach's HCl drops the pH far below amylase's optimal range (6.8), denaturing the enzyme. Starch digestion then resumes only in the duodenum via pancreatic amylase.
Q1.3: If the stomach cannot produce HCl (e.g., due to PPI use), what happens to Enzyme Y?
- Answer: Without HCl, pepsinogen (the inactive form) cannot be activated to pepsin (Enzyme Y). The stomach pH remains near neutral, and even if pepsinogen is secreted, it remains inactive. Protein digestion in the stomach would be severely impaired, though pancreatic proteases in the duodenum would partially compensate.