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Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002.

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Biochemistry. 5th edition.

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Chapter 12Lipids and Cell Membranes

The surface of a soap bubble is a bilayer formed by detergent molecules.

Figure

The surface of a soap bubble is a bilayer formed by detergent molecules. The polar heads (red) pack together leaving the hydrophobic groups (green) in contact with air on the inside and outside of the bubble. Other bilayer structures define the boundary (more...)

The boundaries of cells are formed by biological membranes, the barriers that define the inside and the outside of a cell (Figure 12.1). These barriers prevent molecules generated inside the cell from leaking out and unwanted molecules from diffusing in; yet they also contain transport systems that allow specific molecules to be taken up and unwanted compounds to be removed from the cell. Such transport systems confer on membranes the important property of selective permeability.

Figure 12.1. Red-Blood-Cell Plasma Membrane.

Figure 12.1

Red-Blood-Cell Plasma Membrane. An electron micrograph of a preparation of plasma membranes from red blood cells showing the membranes as seen “on edge,” in cross section. [Courtesy of Dr. Vincent Marchesi.]

Membranes are dynamic structures in which proteins float in a sea of lipids. The lipid components of the membrane form the permeability barrier, and protein components act as a transport system of pumps and channels that endow the membrane with selective permeability.

In addition to an external cell membrane (called the plasma membrane), eukaryotic cells also contain internal membranes that form the boundaries of organelles such as mitochondria, chloroplasts, peroxisomes, and lysosomes. Functional specialization in the course of evolution has been closely linked to the formation of such compartments. Specific systems have evolved to allow targeting of selected proteins into or through particular internal membranes and, hence, into specific organelles. External and internal membranes have essential features in common, and these essential features are the subject of this chapter.

Biological membranes serve several additional important functions indispensable for life, such as energy storage and information transduction, that are dictated by the proteins associated with them. In this chapter, we will examine the general properties of membrane proteins—how they can exist in the hydrophobic environment of the membrane while connecting two hydrophilic environments—and delay a discussion of the functions of these proteins to the next and later chapters.

  • 12.1. Many Common Features Underlie the Diversity of Biological Membranes
  • 12.2. Fatty Acids Are Key Constituents of Lipids
  • 12.3. There Are Three Common Types of Membrane Lipids
  • 12.4. Phospholipids and Glycolipids Readily Form Bimolecular Sheets in Aqueous Media
  • 12.5. Proteins Carry Out Most Membrane Processes
  • 12.6. Lipids and Many Membrane Proteins Diffuse Rapidly in the Plane of the Membrane
  • 12.7. Eukaryotic Cells Contain Compartments Bounded by Internal Membranes
  • Summary
  • Problems
  • Selected Readings

By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

Copyright © 2002, W. H. Freeman and Company.
Bookshelf ID: NBK21199

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