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Difficulty: HardAnimal Nutrition and Digestive System

An experiment was conducted to investigate the rate of protein digestion by incubating boiled egg white with pancreatic juice under different physiological conditions. In tube 1, sodium hydrogen carbonate was added at 37∘C37^\circ\text{C}. In tube 2, dilute hydrochloric acid was added at 37∘C37^\circ\text{C}. In tube 3, sodium hydrogen carbonate was added after boiling the pancreatic juice at 100∘C100^\circ\text{C}. Which of the following observations and physiological explanations correctly accounts for the results?

  1. Rapid digestion occurs only in tube 1 because trypsin and chymotrypsin require an alkaline medium provided by bicarbonate ions at body temperature.Answer
  2. B
    Rapid digestion occurs only in tube 2 because pancreatic enzymes require an acidic medium to convert zymogens into active trypsin.
  3. C
    Digestion in tube 3 is only temporarily delayed because low-temperature inactivation can be reversed upon cooling.
  4. D
    Extracellular digestion occurs equally in tube 1 and tube 3 because pancreatic juice acts saprophytically on non-living substrates.

Answer

Rapid digestion occurs only in tube 1 because pancreatic proteolytic enzymes (such as trypsin) operate optimally in an alkaline environment provided by sodium hydrogen carbonate at optimum body temperature (37°C).
Pancreatic juice contains proteolytic enzymes such as trypsinogen and chymotrypsinogen. In the duodenum, sodium hydrogen carbonate secreted in pancreatic juice neutralizes gastric acid to establish an alkaline pH (pH 7.5−8.0\text{pH } 7.5 - 8.0), which is optimal for pancreatic enzyme activity at body temperature (37∘C37^\circ\text{C}). Tube 1 replicates these optimal physiological conditions, leading to rapid protein hydrolysis.

Step-by-Step Solution

1
Analyze the components of pancreatic juice and their optimal pH environment.
Pancreatic juice contains digestive enzymes like trypsin and chymotrypsin which hydrolyze proteins in the alkaline environment of the duodenum.
Sodium hydrogen carbonate neutralizes acidic chyme from the stomach and provides the alkaline pH needed for pancreatic enzymes.
2
Evaluate the effect of acid in tube 2.
Hydrochloric acid lowers the pH, creating an acidic environment in which trypsin is inactive.
Pancreatic enzymes require alkaline pH, unlike gastric pepsin which functions in acidic pH.
3
Evaluate the effect of thermal denaturation in tube 3.
Boiling pancreatic juice at 100°C permanently denatures the active sites of its enzymes.
High temperatures break hydrogen and disulfide bonds in enzyme tertiary structure, rendering them inactive even if optimal pH is supplied.

Key Concept

Enzyme specificity, pH optima, and thermal denaturation in mammalian digestive tracts
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Animal Nutrition and Digestive System

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