Outline

5.1 Biomembranes: Lipid Composition and Structural Organization

5.2 Biomembranes: Protein Components and Basic Functions

5.3 Organelles of the Eukaryotic Cell

5.4 The Cytoskeleton: Components and Structural Functions

5.5 Purification of Cells and Their Parts

5.6 Visualizing Cell Architecture

▲ FIGURE 5-1 Schematic overview of the major components of eukaryotic cell architecture. The plasma membrane (red) defines the exterior of the cell and controls the movement of molecules between the cytosol and the extracellular medium. Different types of organelles and smaller vesicles enclosed within their own distinctive membranes (black) carry out special functions such as gene expression, energy production, membrane synthesis, and intracellular transport.

function but also play important roles in anchoring proteins to the membrane, modifying membrane protein activities, and transducing signals to the cytoplasm. We then consider the general structure of membrane proteins and how they can relate to different membranes. The unique function of each membrane is determined largely by the complement of proteins within and adjacent to it. The theme of membrane-limited compartments is continued with a review of the functions of various organelles. We then introduce the structure and function of the cytoskeleton, which is intimately associated with all biomembranes; changes in the organization of this filamentous network affect the structure and function of the attached membranes. In the remainder of the chapter, we describe common methods for isolating particular types of cells and subcellular structures and various microscopic techniques for studying cell structure and function.

Fibers of the cytoskeleton (green) provide structural support for the cell and its internal compartments. The internal membranes of organelles and vesicles possess more surface area than that of the plasma membrane but less area than that of the cytoskeleton, as schematically represented by the red, black, and green boxes. The enormous surface area of the cytoskeleton allows it to function as a scaffold on which cellular reactions can take place.

► FIGURE 5-2 The bilayer structure of biomembranes.

(a) Electron micrograph of a thin section through an erythrocyte membrane stained with osmium tetroxide. The characteristic "railroad track" appearance of the membrane indicates the presence of two polar layers, consistent with the bilayer structure for phospholipid membranes. (b) Schematic interpretation of the phospholipid bilayer in which polar groups face outward to shield the hydrophobic fatty acyl tails from water. The hydrophobic effect and van der Waals interactions between the fatty acyl tails drive the assembly of the bilayer (Chapter 2). [Part (a) courtesy of J. D. Robertson.]

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