Overview
This lecture explains how carbohydrates, proteins, and lipids are digested by specific enzymes into smaller molecules that can be absorbed in the small intestine.
Why Large Molecules Need Breaking Down
- Carbohydrates, proteins, and lipids are too large to pass through the small intestine walls.
- These large molecules must be digested into smaller, soluble molecules for absorption.
Enzymes and Their Functions
- Enzymes are proteins that speed up chemical reactions, including digestion.
- Most enzyme names end in "-ase."
Carbohydrate Digestion
- Most dietary carbohydrates are starch, a long polymer of glucose monomers.
- Amylase breaks starch into maltose (two glucose units).
- Maltase breaks maltose into single glucose molecules for absorption.
Protein Digestion
- Proteins from foods like meat and nuts are broken down by protease enzymes.
- Proteases convert proteins into amino acids, which are absorbable.
- Protease is a group name, including enzymes like trypsin and pepsin.
Lipid Digestion
- Lipids (fats and oils) are found in foods like avocados and olive oil.
- Lipase enzymes break lipids into glycerol and fatty acids.
Role of Bile in Digestion
- Bile is not an enzyme but helps digest lipids by emulsifying them.
- Emulsification breaks large lipid droplets into smaller ones, increasing surface area for lipases.
Enzyme Production Locations
- The pancreas and small intestine produce all three types of digestive enzymes.
- Amylase is also made by salivary glands; proteases are also made by the stomach.
Key Terms & Definitions
- Enzyme — a protein that speeds up chemical reactions in the body.
- Amylase — enzyme that breaks starch into maltose.
- Maltase — enzyme that breaks maltose into glucose.
- Protease — enzyme group that breaks proteins into amino acids.
- Lipase — enzyme that breaks lipids into glycerol and fatty acids.
- Bile — a substance that emulsifies lipids, increasing surface area for enzyme action.
Action Items / Next Steps
- Review which enzymes digest each macromolecule and where each is produced.
- Understand the importance of bile in lipid digestion.
- Prepare for questions about enzyme names and functions.