How pepsinogen is converted into pepsin in stomach?

Answer

### Step-by-Step Solution:

1. **Secretion of Pepsinogen**: Pepsinogen is secreted by the gastric chief cells in the stomach lining. It is an inactive precursor (zymogen) of the enzyme pepsin.

2. **Purpose of Inactive Form**: Pepsinogen is secreted in its inactive form to prevent the self-digestion of the stomach wall, which is also made of protein. If pepsin were active in the stomach lining, it could digest the stomach tissue itself.

3. **Activation Process**: The conversion of pepsinogen to pepsin occurs when pepsinogen comes into contact with hydrochloric acid (HCl) present in the gastric juice.

4. **Role of Hydrochloric Acid**: Hydrochloric acid lowers the pH of the stomach contents, creating an acidic environment (approximately pH 1.5 to 3.5) that is necessary for the activation of pepsinogen.

5. **Conversion to Pepsin**: In this acidic environment, pepsinogen undergoes a conformational change and is cleaved to form the active enzyme pepsin. This process involves the removal of a small peptide from the pepsinogen molecule.

6. **Function of Pepsin**: Once activated, pepsin can then begin the digestion of proteins in the food by breaking them down into smaller peptides.

### Summary:
Pepsinogen is secreted in an inactive form to protect the stomach lining from self-digestion. It is activated to pepsin in the presence of hydrochloric acid, which provides the necessary acidic environment for the conversion.

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