Digestive enzymes
The groups of enzymeA protein which catalyses or speeds up a chemical reaction. involved in the breakdown of food are:
carbohydraseEnzyme that breaks down carbohydrates. break down carbohydrateFood belonging to the food group consisting of sugars, starch and cellulose. Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess. In plants, carbohydrates are important for photosynthesis.:
\(\textup{carbohydrate}\xrightarrow[]{\textup{carbohydrase}} \textup{simple~sugars}\)
Starch is a type of carbohydrate. The carbohydrase that breaks down starch is amylaseAn enzyme that can break down starch into simple sugars.:
\(\textup{starch}\xrightarrow[]{\textup{amylase}} \textup{glucose}\)
proteaseEnzyme that breaks down proteins. break down proteinOrganic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair.:
\(\textup{protein}\xrightarrow[]{\textup{protease}} \textup{amino~acids}\)
lipaseEnzyme that breaks down lipids (fats and oils). break down lipidFat or oils, composed of fatty acids and glycerol.
\(\textup{lipid}\xrightarrow[]{\textup{lipase}} \textup{fatty acids} + \textup{glycerol}\)
Carbohydrases
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 substrateA substance on which enzymes act. in the early part of digestion for enzyme action. Digestion by carbohydrase enzymes breaks down very large starch molecules to small glucoseA simple sugar used by cells for respiration. molecules.
| 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 |
| Region of digestive system | Mouth |
|---|---|
| Enzyme | Salivary amylase |
| Where produced | Salivary glands |
| Substrate | Starch |
| Broken down into | Maltose |
| Region of digestive system | Small intestine - duodenum |
|---|---|
| Enzyme | Pancreatic amylase |
| Where produced | Pancreas |
| Substrate | Starch |
| Broken down into | Maltose |
| Region of digestive system | Small intestine - ileum |
|---|---|
| Enzyme | Amylase |
| Where produced | Wall of ileum |
| Substrate | Maltose |
| Broken down into | Glucose |
Proteases
Proteases break down proteins in several regions of the digestive system.
Digestion by protease enzymes breaks down proteins to amino acidThe building blocks that make up a protein molecule.. Cells use amino acids to make new proteins. The liver breaks down unwanted amino acids to ureaA nitrogenous waste product resulting from the breakdown of proteins. It is excreted in urine., which is then carried by the blood to the kidneys. The kidneys excrete urea in solution as urine.
| 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 |
| Region of digestive system | Stomach |
|---|---|
| Enzyme | Protease - pepsin |
| Where produced | Gastric glands in stomach |
| Substrate | Proteins |
| Broken down into | Begins the breakdown into amino acids |
| Region of digestive system | Small intestine - duodenum |
|---|---|
| Enzyme | Protease - trypsin |
| Where produced | Pancreas |
| Substrate | Proteins |
| Broken down into | Continues the breakdown into amino acids |
| Region of digestive system | Small intestine - ileum |
|---|---|
| Enzyme | Protease - peptidase |
| Where produced | Wall of ileum |
| Substrate | Peptides |
| Broken down into | Completes the breakdown into amino acids |
Lipases
Lipases break down lipids in one region of the digestive system.
Digestion by lipase enzymes breaks down lipids to glycerolPropane-1,2,3-triol. It reacts with fatty acids to form esters, found in nature as fats and oils. and fatty acids. Cells reform fats from the fatty acids and glycerol molecules.
| Region of digestive system | Enzyme | Where produced | Substrate | Broken down into |
| Small intestine - duodenum | Lipase | Pancreas | Lipids | Fatty acids and glycerol |
| Region of digestive system | Small intestine - duodenum |
|---|---|
| Enzyme | Lipase |
| Where produced | Pancreas |
| Substrate | Lipids |
| Broken down into | Fatty acids and glycerol |
Learn all about enzymes with Dr Alex Lathbridge.
Listen to the full series on 大象传媒 Sounds.
In this podcast, learn the key facts about enzymes. Listen to the full series on 大象传媒 Sounds.