Digestive Enzymes and Their Actions: Complete Chart Guide

Digestive enzymes are protein molecules that speed up the chemical breakdown of food into tiny, soluble pieces. A piece of bread or meat is far too large to enter your blood, but enzymes cut it step by step until only glucose, amino acids, fatty acids and glycerol remain.

Knowing which enzyme acts where matters because digestion is orderly, not random. Each enzyme works only on one type of food and only at a certain acidity, so the gut changes its conditions from region to region to let the right enzyme work.

Key Concepts

An enzyme is a biological catalyst that remains unchanged after the reaction. Amylases digest starch, proteases digest proteins, and lipases digest fats. The mouth and pancreas make amylase; the stomach makes pepsin, a protease that needs acid. The pancreas makes trypsin and lipase, which need alkaline conditions. The small intestine completes digestion with enzymes like maltase, lactase, sucrase and peptidases fixed on its wall.

• Salivary amylase (ptyalin): acts in mouth at near-neutral pH, converts starch to maltose.
• Pepsin: acts in stomach at pH 1.5 to 2, converts proteins to peptides.
• Trypsin: acts in duodenum at pH 7.5 to 8, converts proteins and peptides to smaller peptides.
• Pancreatic lipase: acts on emulsified fat to give fatty acids and glycerol.
• Lactase: splits milk sugar lactose into glucose and galactose.

Formulas

The key reactions can be written simply. Starch breakdown: starch + water → maltose, catalysed by amylase. Protein breakdown: protein + water → peptides → amino acids, catalysed by pepsin, trypsin and peptidases. Fat breakdown: fat + water → fatty acids + glycerol, catalysed by lipase. Disaccharide breakdown: maltose → glucose + glucose by maltase, lactose → glucose + galactose by lactase, and sucrose → glucose + fructose by sucrase. Water is a reactant in every case because these are hydrolysis reactions, and each enzyme works best only near its optimum pH and at body temperature around 37 °C.

Worked Example

Suppose you eat 50 grams of starch in rice. Salivary amylase starts cutting it in the mouth for a brief minute before stomach acid stops it. In the duodenum, pancreatic amylase resumes and converts nearly all the remaining starch to maltose. Maltase on the intestinal wall then splits each maltose into two glucose molecules. Since starch is built from glucose units, 50 grams of starch yields roughly 55 grams of glucose after water is added across bonds. This glucose is absorbed and raises blood sugar, which is why rice gives quick energy. If lactase is missing, the same logic fails for milk: lactose stays undigested and causes gas and diarrhoea.

Common Misconceptions

• Misconception: One enzyme digests all foods. Correction: Enzymes are specific; amylase cannot cut protein and lipase cannot cut starch.
• Misconception: Enzymes are used up in digestion. Correction: They are catalysts and are reused many times until denatured by wrong pH or heat.
• Misconception: The stomach digests starch well. Correction: Its strong acid inactivates salivary amylase, so starch digestion pauses there.

Real-World Applications

Lactose-free milk is made by adding lactase enzyme in factories for people who cannot digest lactose. Washing powders use similar proteases and lipases to remove food stains. Doctors prescribe enzyme supplements for pancreatic insufficiency and test enzyme levels to diagnose organ damage. In food industries, amylases convert starch to sweet syrups.

Digestive enzymes thus form an assembly line: amylases, proteases and lipases cut large food molecules in stages, each at its favourite pH, until only absorbable building blocks remain.