An enzyme acts on a substrate and makes products, and the enzyme itself is not used up. Keep three columns in your notes: enzyme, substrate, product.
This lesson is part of nutrition and digestion. Enzyme properties are covered in metabolism and enzymes.
Which enzyme acts on which substrate?
| Enzyme | Substrate | Product | Where |
|---|---|---|---|
| Amylase | Starch | Maltose | Mouth, small intestine |
| Maltase | Maltose | Glucose | Small intestine |
| Pepsin | Protein | Polypeptides | Stomach |
| Trypsin | Protein | Polypeptides | Small intestine |
| Peptidase | Polypeptides | Amino acids | Small intestine |
| Lipase | Fats | Fatty acids and glycerol | Small intestine |
Read each row as: enzyme acts on substrate to give product.
Worked example: why does rice taste sweeter?
An original observation: a student chews a piece of rice for two minutes and notices a slightly sweet taste. Explain why.
Rice contains starch. Salivary amylase in the mouth acts on the starch, the substrate, and breaks it into maltose, the product. Maltose is a sugar, so it tastes sweet.
The enzyme is not used up, so the same amylase molecules keep acting on more starch while the rice is chewed.
The mistake that swaps the roles
A student writes “amylase is broken down to maltose”. Here the enzyme has been written as the substrate. The enzyme is not changed.
The fix is to write “amylase breaks down starch to maltose”, with the substrate after “breaks down” and the product after “to”.
Why are enzymes specific?
The active site of an enzyme has a particular shape. Only a substrate that fits the active site binds, forming an enzyme-substrate complex.
That is why amylase acts on starch and not on protein. A substrate of the wrong shape does not fit.
A self-check question
Complete the sentence: “Lipase acts on ______ to form ______ and ______.” Then state why lipase does not act on starch.
Answer
Lipase acts on fats to form fatty acids and glycerol. Lipase does not act on starch because the shape of its active site fits fats but not starch, so starch cannot bind.
See where these enzymes act in tracing digestion through the alimentary canal. The biological data interpretation trainer offers more practice.
If the three columns still blur, SPM Biology one-to-one tuition lets a teacher quiz you on fresh examples.