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1.17: Enzymes

Difficulty Level: At Grade Created by: CK-12
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What is a biological catalyst?

This super fast train can obviously reach great speeds. And there's a lot of technology that helps this train go fast. Speaking of helping things go fast brings us to enzymes. Life could not exist without enzymes. Essentially, enzymes are biological catalysts that speed up biochemical reactions.


Enzymes and Biochemical Reactions

Most chemical reactions within organisms would be impossible under the conditions in cells. For example, the body temperature of most organisms is too low for reactions to occur quickly enough to carry out life processes. Reactants may also be present in such low concentrations that it is unlikely they will meet and collide. Therefore, the rate of most biochemical reactions must be increased by a catalyst. A catalyst is a chemical that speeds up chemical reactions. In organisms, catalysts are called enzymes. Essentially, enzymes are biological catalysts.

Like other catalysts, enzymes are not reactants in the reactions they control. They help the reactants interact but are not used up in the reactions. Instead, they may be used over and over again. Unlike other catalysts, enzymes are usually highly specific for particular chemical reactions. They generally catalyze only one or a few types of reactions.

Enzymes are extremely efficient in speeding up reactions. They can catalyze up to several million reactions per second. As a result, the difference in rates of biochemical reactions with and without enzymes may be enormous. A typical biochemical reaction might take hours or even days to occur under normal cellular conditions without an enzyme, but less than a second with an enzyme.

Enzymes, an overview of these proteins, can be viewed at http://www.youtube.com/watch?v=E90D4BmaVJM&feature=related (9:43).

As you view Enzymes, focus on these concepts:

  1. the role of enzymes in nature,
  2. other uses of enzymes.

Importance of Enzymes

Enzymes are involved in most of the chemical reactions that take place in organisms. About 4,000 such reactions are known to be catalyzed by enzymes, but the number may be even higher.

In animals, an important function of enzymes is to help digest food. Digestive enzymes speed up reactions that break down large molecules of carbohydrates, proteins, and fats into smaller molecules the body can use. Without digestive enzymes, animals would not be able to break down food molecules quickly enough to provide the energy and nutrients they need to survive.


  • Enzymes are biological catalysts. They speed up biochemical reactions.
  • Enzymes are involved in most of the chemical reactions that take place in organisms.


Use this resource to answer the questions that follow.

  1. What are enzymes?
  2. What are substrates? What is the enzyme-substrate complex?
  3. How do enzymes work?
  4. What happens to the enzyme during a reaction?


1. What are enzymes?

2. Explain why organisms need enzymes to survive.

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catalyst A substance that increases (or decreases) the rate of a chemical reaction but is not used up in the reaction.
enzyme Biological catalyst; protein that accelerates a biochemical reaction.

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Difficulty Level:
At Grade

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Date Created:
Feb 24, 2012
Last Modified:
Oct 03, 2016
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