Which of following processes occurring in the stomach is autocatalysis?

Options

A. Low pH denaturing the proteinaceous substances in food.
B. Low PH activating pepsinogen to pepsin.
C. Absorption of monomeric molecules in chyme.
D. Pepsin activating more pepsinogen molecules.

Answer

To determine which process occurring in the stomach is autocatalysis, we need to understand the concept of autocatalysis and analyze the options provided.

### Step-by-Step Solution:

1. **Understanding Autocatalysis**:
- Autocatalysis is a process where a product of a reaction acts as a catalyst for that same reaction, thereby accelerating the reaction without the need for an external catalyst.

2. **Analyzing the Options**:
- **Option 1**: Low pH denaturing protein substances in food.
- This process involves the unfolding of proteins due to the acidic environment but does not involve a product catalyzing its own formation. Thus, it is not autocatalysis.

- **Option 2**: Low pH activating pepsinogen to pepsin.
- Pepsinogen is an inactive enzyme that gets activated to pepsin in the presence of HCl. However, this activation is not autocatalytic because it requires HCl as an external factor. Therefore, this is not autocatalysis.

- **Option 3**: Absorption of monomeric molecules in the stomach.
- This process refers to the absorption of nutrients and does not involve any catalytic reaction, hence it cannot be classified as autocatalysis.

- **Option 4**: Pepsin activating more pepsinogen molecules.
- This is the correct process of autocatalysis. Once pepsin is activated from pepsinogen, it can further catalyze the conversion of more pepsinogen into pepsin. Here, the product (pepsin) facilitates the conversion of more of its precursor (pepsinogen) into itself, making it an autocatalytic process.

3. **Conclusion**:
- The process occurring in the stomach that is autocatalysis is **Option 4: Pepsin activating more pepsinogen molecules**.

### Final Answer:
The correct answer is **Option 4**: Pepsin activating more pepsinogen molecules.

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