Enzymes and Digestion

As we know enzymes are important molecules, they are particularly important in digestion as they help break down large, insoluble food molecules into small, soluble molecules which can be easily absorbed.  Enzymes work best at their optimum pH.  So for example if the stomach does not produce enough HCl, the enzyme, pepsin, will not work properly, (remember the optimum pH for pepsin is 2).

There are 3 main types of enzymes in our gut:  Protease, Carbohydrase, and Lipase.



Protease enzymes are secreted by the stomach, pancreas and small intestine and their job is to digest proteins.  An example of a protease is pepsin which is secreted in the stomach. Proteins are long chains of amino acids, and protease enzymes break them into peptides (smaller chains of amino acids molecules) and eventually into individual amino acids, which are small and easily absorbed in the small intestine. The word equation for the protease reaction is:

proteins amino acids



Carbohydrase enzymes are secreted by the mouth, pancreas and small intestine.  The carbohydrase enzyme, amylase is secreted by the mouth and found in saliva. It starts to work as soon as we begin to chew our food.  Amylase digests long, complex starch (polysaccharide) molecules, into smaller, simpler maltose (disaccharide) molecules. As maltose is a disaccharide it still needs further digestion before it can be absorbed.  The enzyme maltase breaks it down into glucose.  The word equation is:

starch maltose glucose

Other dietary sugars such as sucrose and lactose (both disaccharides) are broken down further by different carbohydrase enzymes. The word equations are:

sucrose glucose + fructose

lactose glucose + galactose



Lipase is secreted by the pancreas and the walls of the small intestine. It digests complex fat (or lipid) molecules into simple, soluble fatty acid and glycerol molecules. The word equation for this reaction is:

Lipids fatty acids + glycerol

NOTE: It’s important you recall the main digestive enzymes, the food types they break down and where they are produced.


Summary Table of the Digestive Enzymes

Digestive enzyme Produced in Reaction catalysed
Protease (e.g. Pepsin) Stomach, pancreas and small intestine Protein Amino acids
Carbohydrase (e.g. Amylase) Salivary glands, pancreas and small intestine Starch Glucose
Lipase (e.g. Gastric lipase) Pancreas and small intestine Fats (lipids) Fatty acid and glycerol