How are macromolecules in food broken down into monomers in the small intestine, and which enzymes are involved?

Sourav PanNovember 8, 2024

Answered

In the small intestine, macromolecules in food are broken down into their respective monomers through a series of enzymatic reactions. This process involves several types of enzymes that target specific macromolecules: carbohydrates, proteins, and lipids. Here’s a detailed overview of how this breakdown occurs and the enzymes involved:

1. Carbohydrate Digestion

Carbohydrates, primarily in the form of polysaccharides and disaccharides, are broken down into monosaccharides (simple sugars) through hydrolysis reactions facilitated by specific enzymes.

• Enzymes Involved:
  • Amylase: Secreted by the pancreas, amylase continues the breakdown of starches into maltose (a disaccharide) after initial digestion begins in the mouth.
  • Maltase: Breaks down maltose into two glucose molecules.
  • Sucrase: Converts sucrose (table sugar) into glucose and fructose.
  • Lactase: Breaks down lactose (milk sugar) into glucose and galactose.

These enzymes are present in the brush border of the intestinal lining, where they act on the chyme as it passes through the small intestine. The resulting monosaccharides are then absorbed into the bloodstream for use by the body’s cells.

2. Protein Digestion

Proteins are broken down into smaller peptides and eventually into amino acids through a series of enzymatic actions.

• Enzymes Involved:
  • Trypsin, Chymotrypsin, and Elastase: These proteases are produced by the pancreas and released into the duodenum. They act on proteins to reduce them to smaller peptides.
  • Carboxypeptidase: This enzyme further breaks down peptides by removing terminal amino acids from the peptide chain.
  • Aminopeptidase and Dipeptidase: These enzymes act on small peptides to release free amino acids.

The breakdown of proteins is crucial for providing amino acids that can be absorbed directly into the bloodstream.

3. Lipid Digestion

Lipids, primarily in the form of triglycerides, are emulsified by bile salts and then broken down into fatty acids and glycerol.

• Enzymes Involved:
  • Lipase: Secreted by the pancreas, lipase hydrolyzes triglycerides into monoglycerides and free fatty acids. This process is enhanced by bile salts that form micelles, aiding in lipid absorption.

The resulting fatty acids and monoglycerides can diffuse across the intestinal cell membranes for absorption .

Summary of Processes

• Hydrolysis Reactions: The process of breaking down macromolecules involves hydrolysis reactions, where water molecules are used to cleave bonds between monomers. For example:
  • Carbohydrates are broken down from polysaccharides to monosaccharides.
  • Proteins are reduced from polypeptides to amino acids.
  • Lipids are split into fatty acids and glycerol.

These reactions release energy stored in macromolecules and allow for their absorption through the intestinal walls