Protein Digestion and Absorption

Overview

• Proteins are composed of amino acids linked by peptide bonds.
• Digestion and absorption occur through a series of steps involving different organs and enzymes.

Digestive Tract Overview

• Organs involved: esophagus, stomach, small intestine (duodenum), and large intestine.
• Proteins are found in foods like meat.

Protein Structure

• Proteins have an amino terminal (amine group) and a carboxy terminal (carboxy group).
• Amino acids link together via these groups.

Digestion Process

Mouth

• Initial physical digestion through mastication (chewing).

Stomach

• Chemical digestion begins:
  • Secretion of pepsinogen, which converts to pepsin in the presence of hydrochloric acid.
  • Pepsin breaks down proteins into large polypeptides.

Small Intestine (Duodenum)

• Main site for protein digestion and absorption.
• Pancreatic enzymes are secreted:
  • Trypsinogen, chymotrypsinogen, and procarboxypeptidase are secreted as zymogens (inactive precursors).
• Activation of enzymes:
  • Enteropeptidase activates trypsinogen to trypsin.
  • Trypsin activates other zymogens (chymotrypsinogen to chymotrypsin and procarboxypeptidase to carboxypeptidase).

Enzyme Functions

• Trypsin: Hydrolyzes peptide bonds, stimulates its own production, and activates other enzymes.
• Chymotrypsin: Similar function to trypsin.
• Carboxypeptidase: Hydrolyzes peptide bonds from the carboxy end.
• Brush border enzymes:
  • Dipeptidases: Hydrolyze dipeptides.
  • Aminopeptidases: Hydrolyze peptide bonds from the amino terminal.

Absorption

• Tripeptides and dipeptides:
  • Absorbed via co-transport with hydrogen ions.
  • Once inside the cell, they are further broken down into amino acids.
• Amino acids:
  • Absorbed through co-transport with sodium ions.
  • Result in net absorption of sodium and water.

Transport to the Liver

• Amino acids enter the bloodstream and are transported to the liver.
  • Used for protein synthesis or storage.

Summary

• Protein digestion and absorption involve multiple enzymes and transport mechanisms.
• The process ensures amino acids are available for the body’s needs.

End of Video

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