Examkin

Question

Difficulty: MediumAnimal Nutrition and Digestive System

A mixture of starch and protein was treated with pancreatic juice in a test tube maintained at 0∘C0^\circ\text{C} and optimal pH\text{pH} for two hours, resulting in no breakdown of either substrate. When the temperature of the mixture was subsequently raised to 37∘C37^\circ\text{C}, rapid digestion of both starch and protein was observed. Which of the following best explains why digestion occurred after the mixture was warmed?

  1. Low temperatures temporarily render enzymes inactive without destroying their structural integrity, allowing activity to resume upon warming.Answer
  2. B
    The low temperature permanently denatured the digestive enzymes, but heating restored their native tertiary protein structures.
  3. C
    The enzymes degraded into saprophytic nutrients at low temperatures, which were then holozoically reassembled during heating.
  4. D
    Freezing conditions destroy the enzyme active sites, requiring thermal energy to synthesize new functional active sites from the substrate.

Answer

Low temperatures temporarily render enzymes inactive without destroying their structural integrity, allowing activity to resume upon warming.
At 0∘C0^\circ\text{C}, enzymes like pancreatic amylase and trypsin lose kinetic energy, reducing the rate of effective collisions with substrate molecules. Because low temperature does not disrupt tertiary protein structure, the enzyme is merely inactivated, not denatured. Restoring the temperature to 37∘C37^\circ\text{C} restores kinetic motion and catalytic capability.

Step-by-Step Solution

1
Analyze the effect of low temperature (0∘C0^\circ\text{C}) on enzyme molecules.
Enzymes experience reduced kinetic energy, drastically lowering substrate collision frequency without altering their active site conformation.
Temperature affects molecular velocity, but low temperatures do not break the covalent or hydrogen bonds maintaining enzyme tertiary structure.
2
Evaluate the effect of raising the temperature to the optimal level (37∘C37^\circ\text{C}).
Kinetic energy increases, leading to frequent effective collisions between active sites and substrate molecules.
Since the enzymes remained intact during the cold phase, warming restores catalytic function instantly.

Key Concept

Effect of Temperature on Digestive Enzyme Activity and Reversibility of Low-Temperature Inactivation
Rate this question

Topics

Animal Nutrition and Digestive System

More questions from this topic