An enzyme molecule is like a lock.
The substrate molecule has a complementary shape to the enzyme, and can fit into it like a key.
enzyme
The enzyme changes the substrate into new molecules called products.
The substrate must be a perfect fit.
Figure 5.2 The lock and key mechanism.
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All enzymes have active sites. Each enzyme has an active site that exactly fits its substrate. This means that each enzyme can only act on a particular kind of substrate. Amylase, for example, cannot break down protein molecules, because they do not fit into its active site. substrate (starch)
enzyme (amylase)
product
active site
The substrate molecule (starch in this case) slots into the active site.
Each enzyme has an active site into which its substrate molecule fits exactly. This enzyme is amylase, and its active site is just the right size and shape for a starch molecule.
The starch is split into maltose molecules. The enzyme is unaltered, and ready to accept another part of the starch molecule.
Figure 5.3 How an enzyme works.
Questions 5.1 What is a catalyst? 5.2 What are the catalysts inside a living organism called? 5.3 Which kinds of reaction inside a living organism are controlled by enzymes?
5.4 What is meant by a carbohydrase? 5.5 Give one example of a carbohydrase. 5.6 Name the substrate and product of a reaction involving a carbohydrase.
Original material © Cambridge University Press 2014
Chapter 5: Enzymes
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