Basic Concepts and Kinetics of Enzymes

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CHAPTER 6 Basic Concepts of Enzyme Action
CHAPTER 7 Kinetics and Regulation
CHAPTER 8 Mechanisms and Inhibitors
CHAPTER 9 Hemoglobin, an Allosteric Protein

In Section 2, we considered the chemical workhorses of life—proteins. In this section, we examine an important class of proteins called enzymes. Protein enzymes are the most prominent catalysts of biological systems. Catalysts are chemicals that enhance the rate of reactions without being permanently altered themselves. The role of enzymes, then, is to make biochemically required reactions take place at a rate compatible with life.

Proteins as a class of macromolecules are well suited to be catalysts because of their capacity to form complex three-dimensional structures that can recognize one or a few molecules with high specificity. Collectively, the range of molecules on which enzymes can act is virtually unlimited. Because of their specificity, enzymes bring substrates (reactants) together at a particular site on the enzyme, called the active site, where they are oriented to facilitate the making and breaking of chemical bonds. The most striking characteristics of enzymes are their catalytic power and specificity.

Some enzymes are information sensors as well as catalysts. In addition to active sites, allosteric enzymes have distinct regulatory sites that bind to environmental signals. This binding modifies the activity of the active site.

We begin this section with a look at the basic properties of enzymes, with special emphasis on the energetics of enzyme-catalyzed reactions. We then move on to a kinetic analysis of enzymes. Next, we see how enzyme activity is modified by environmental conditions and examine the mechanism of action of chymotrypsin, a protein-digesting enzyme. We end the section with an examination of hemoglobin. This oxygen-transporting protein is a source of insight into the properties of allosteric proteins.

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✓ By the end of this section, you should be able to: