The major nutrients required for a healthy diet are carbohydrates, proteins and lipids. The digestive system breaks down large molecules of food, which are then absorbed into the bloodstream.
The groups of enzymes involved in the breakdown of food are:
Carbohydrases break down carbohydrates:
\[\mathbf{carbohydrate}\; \overset{\mathbf{carbohydrase}}{\rightarrow}\; \mathbf{simple\; sugars}\]
Starch is a type of carbohydrate. The carbohydrase that breaks down starch is amylase:
\[\mathbf{starch}\; \overset{\mathbf{amylase}}{\rightarrow}\; \mathbf{glucose}\]
Proteases break down proteins:
\[\mathbf{protein}\; \overset{\mathbf{protease}}{\rightarrow}\; \mathbf{amino\; acids}\]
\[\mathbf{lipid}\; \overset{\mathbf{lipase}}{\rightarrow}\; \mathbf{fatty\; acids}\;\mathbf{+\; glycerol}\]
Carbohydrases break down carbohydrates in several regions of the digestive system.
Most of the carbohydrate we eat is starch, so this will be the main substrate in the early part of digestion for enzyme action.
| Region of digestive system | Enzyme | Where produced | Substrate | Broken down into |
|---|---|---|---|---|
| Mouth | Salivary amylase | Salivary glands | Starch | Maltose |
| Small intestine - Duodenum | Pancreatic amylase | Pancreas | Starch | Maltose |
| Small intestine - Ileum | Amylase | Wall of ileum | Maltose | Glucose |
Proteases break down proteins in several regions of the digestive system.
| Region of digestive system | Enzyme | Where produced | Substrate | Broken down into |
|---|---|---|---|---|
| Stomach | Protease - pepsin | Gastric glands in stomach | Proteins | Begins the breakdown into amino acids |
| Small intestine - Duodenum | Protease - trypsin | Pancreas | Proteins | Continues the breakdown into amino acids |
| Small intestine - Ileum | Protease - peptidase | Wall of ileum | Peptides | Completes the breakdown into amino acids |
Lipases break down lipids in one region of the digestive system.
| Region of digestive system | Enzyme | Where produced | Substrate | Broken down into |
|---|---|---|---|---|
| Small intestine - Duodenum | Lipase | Pancreas | Lipids | Fatty acids and glycerol |