The
Figure 2.16: A healthy diet includes protein, fat, and carbohydrate. ( 27 )Enzyme Reactions
The oxidation reaction occurs readily, but not all reactions move so quickly. Others can take
quite a while. Since many of the body’s necessary chemical reactions would take years to
happen on their own, you need the help of enzymes.Enzymesspeed up chemical reactions,
often by bringing the reactants closer together so they can interact more easily (Figure
2.17). Enzymes attach to, orbind, specifically to the reactants. Because enzymes are so
specific, you have a different enzyme for every chemical reaction in your body. A single cell
may contain hundreds or thousands of different enzymes.
When an enzymes attaches, or binds, to another molecule, that molecule is referred to as
thesubstrate. The enzyme is usually much bigger than the substrate.
How Enzymes Work
How do enzymes speed up biochemical reactions so dramatically? Like all catalysts, en-
zymes work by lowering the activation energy of chemical reactions. This is illustrated in
Figure2.18. The biochemical reaction shown in the figure requires about three times as
much energy without the enzyme as it does with the enzyme. An animation of this pro-
cess can be viewed athttp://www.stolaf.edu/people/giannini/flashanimat/enzymes/
transition%20state.swf.