Enzymes as Catalysts

I. Enzymes are biological catalysts.

A. Catalysts increase the rate of chemical reactions.

1. A catalyst is not altered by the reaction.

2. A catalyst does not change the final result of a reaction.

B. Catalysts lower the activation energy of chemical reactions.

1. The activation energy is the amount of energy needed by the reactant molecules to participate in a reaction.

2. In the absence of a catalyst, only a small proportion of the reactants possess the activation energy to participate.

3. By lowering the activation energy, enzymes allow a larger proportion of the reactants to participate in the reaction, thus increasing the reaction rate.

II. Most enzymes are proteins.

A. Protein enzymes have specific three-dimensional shapes that are determined by the amino acid sequence and, ultimately, by the genes.

B. The reactants in an enzyme-catalyzed reaction—called the substrates of the enzyme—fit into a specific pocket in the enzyme called the active site.

C. By forming an enzyme-substrate complex, substrate molecules are brought into proper orientation and existing bonds are weakened. This allows new bonds to be formed more easily.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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