The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
The plasma membrane is a very thin, continuous sheet of phospholipids and proteins that surrounds all living cells and separates them from their external environment. This membranous barrier maintains conditions within the cell and creates an internal chemical environment essential for life. It is one of the few structures common to every living cell. Invisible except in an electron microscope, a plasma membrane is typically only 4-5 nm thick. In spite of its thinness, however, the plasma membrane is surprisingly strong, flexible, and stretchable. It has a high electrical insulating capacity, and a remarkable ability to self-assemble to repair breaks and damage.
Structurally, almost all plasma membranes are composed of a double layer of phospholipid molecules arranged with their hydrophobic (water-hating) lipid tails oriented toward the membrane interior and their hydrophilic (water-loving) heads making up the opposing membrane surfaces. A wide variety of globular proteins are embedded in or on this biomolecular lipid leaflet structure, some of them reaching completely across the membrane while others are implanted in or attached to either the extra-cellular or intra-cellular surface. These proteins not only help create the structure of the membrane but also carry out enzyme reactions or provide channels for transport of selected materials into or out of the cell. Integral membrane proteins can serve as recognition and binding sites for the cell to its neighbors or substrates. They also act as receptors for extracellular molecules that serve as signals, nutrients, or serve other important functions.