Chapter 4The Structure And Function Of The Plasma Membrane

Chapter 4The Structure And Function Of The Plasma Membrane...

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Chapter 4 The Structure And Function Of The Plasma Membrane First Detection of Cell Membrane I. Cells are separated from the world by a thin, fragile structure, the plasma membrane – 5 – 10 nm thick A. ~10,000 plasma membranes stacked one on top of another would equal the thickness of a book's page B. No hint of a plasma membrane is detected in a thin section under a light microscope since it is so thin C. Finally, in the late 1950s, techniques for preparing & staining tissues had progressed to the point where they could be visualized in the electron microscope 1. J. D. Robertson (Duke Univ.) – portrayed plasma membrane as three-layered structure, consisting of 2. All membranes examined closely (plasma, nuclear or cytoplasmic) or from plants, animals or microorganisms had the same ultrastructure 3. The pictures touched off a vigorous debate as to the molecular composition of the various layers of the membrane 4. The 2 dark-staining layers in the electron micrographs correspond primarily to the inner & outer polar surfaces of the bilayer Summary of Membrane Functions and Overview of Membrane Structure I. Compartmentalization - membranes enclose entire cell or diverse intracellular spaces in which occur A. They are continuous, unbroken sheets B. A cell's various membrane-bound compartments have markedly different contents II. Scaffold for biochemical activities – membranes are also distinct compartments themselves A. They provide cell with extensive framework (scaffolding) within which components can be ordered for effective interaction III. Provide selectively permeable barrier – membrane can be compared to moat around a castle; a general A. They prevent the unrestricted exchange of molecules from one side to the other - control what gets into & out of cell; H 2 O moves easily B. They also provide the means of communication between the compartments they separate IV. Transporting solutes – they have transport machinery to move substances from one side to the other A. Can transport substances (ions, sugars, amino acids, etc.) up or down concentration gradient; sugars & B. Can establish ionic gradients across itself (critical for nerves, muscles, maybe helps all cells respond to their environment) by transporting specific ions V. Response to external signals ( signal transduction ) plays critical role in response to external stimuli (hormones, growth factors, neurotransmitters) A. Receptors in membrane combine with specific molecules ( ligands ) having complementary structure & then initiate response 1.
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This note was uploaded on 09/10/2008 for the course BIO 201 taught by Professor Janicke during the Spring '08 term at SUNY Buffalo.

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Chapter 4The Structure And Function Of The Plasma Membrane...

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