Biochemical Processes in Digestion

Overview

• Digestion involves the breakdown of large molecules (macromolecules) into their base units (monomers) for absorption.
• Enzymes involved are intrinsic, secreted by the GI tract or accessory glands.
• Hydrolysis: Chemical process using water to break down molecules.

Carbohydrate Digestion

• Begins in the mouth with the enzyme salivary amylase breaking down polysaccharides (starch, glycogen).
• Monosaccharides (glucose, fructose, galactose) are absorbed.
• Pancreatic amylase works in the duodenum to further digest polysaccharides to oligosaccharides.
• Brush border enzymes (dextrinase, glucoamylase) convert oligosaccharides to disaccharides.
• Enzymes like lactase, maltase, sucrase break disaccharides to monosaccharides.

Protein Digestion

• Begins in the stomach with low pH denaturing proteins.
• Pepsin is activated from pepsinogen in the stomach, breaking down polypeptides to oligopeptides.
• In the small intestine, pancreatic proteases (trypsin, chymotrypsin) further digest proteins.
• Carboxypeptidase and aminopeptidase break peptides at carboxyl and amino ends, respectively.
• Dipeptidases break down dipeptide bonds.
• Amino acid absorption uses secondary active transport due to sodium ion gradient.

Lipid Digestion

• Lingual lipase starts digestion in the stomach at lower pH.
• Gastric lipase in the stomach does minimal digestion.
• Bile salts in the small intestine emulsify fats, increasing surface area for digestion.
• Pancreatic lipases break triglycerides into monoglycerides and fatty acids.
• Absorption involves micelles and the lymphatic system.

Nucleic Acid Digestion

• Enzymes include pancreatic ribonucleases and deoxyribonucleases.
• Breakdown of nucleotides into monomers.
• Brush border enzymes (nucleosidases, phosphatases) break down monomers into pentose sugars, phosphate ions, and nitrogenous bases.