7.4 Chemical Digestion: The Molecular Scissors
Breaking down LARGE INSOLUBLE molecules → SMALL SOLUBLE molecules (ready for absorption)
What is Chemical Digestion?
DEFINITION: The breakdown of LARGE INSOLUBLE molecules into SMALL SOLUBLE molecules
WHY? Only small, soluble molecules can be ABSORBED through the intestine wall into the blood!
AMYLASE
SUBSTRATE: Starch
Starch → MALTOSE → GLUCOSE
MADE IN: Salivary glands, Pancreas
ACTS IN: Mouth, Duodenum
PROTEASE
SUBSTRATE: Protein
Protein → AMINO ACIDS
MADE IN: Stomach, Pancreas
ACTS IN: Stomach, Small intestine
⚠️ SUPPLEMENT:
• PEPSIN: Stomach (pH 2)
• TRYPSIN: Small intestine (pH 8)
LIPASE
SUBSTRATE: Fats & Oils
Fats → FATTY ACIDS + GLYCEROL
MADE IN: Pancreas
ACTS IN: Small intestine
🧪 pH Control System
🔴 HYDROCHLORIC ACID (HCl)
- • Creates pH 2 in stomach
- • KILLS BACTERIA in food
- • Provides acidic pH for PEPSIN
🟢 BILE
- • ALKALINE mixture
- • NEUTRALIZES stomach acid
- • Provides alkaline pH (pH 8) for intestinal enzymes
🎯 EXAMINER TRAPS
❌ "Amylase is made in the pancreas, so it acts in the pancreas"
✅ CORRECT: Pancreas MAKES it, but releases it into the DUODENUM. Food never enters the pancreas!
❌ "Amylase breaks down starch into glucose"
✅ CORRECT: Amylase breaks starch into MALTOSE. Then maltase breaks maltose into glucose.
❌ "Bile is an enzyme"
✅ CORRECT: Bile is NOT an enzyme! It's an alkaline mixture that neutralizes acid.
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