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9-15 - The Structure and Function of the Plasma Membrane...

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The Structure and Function of the Plasma Membrane During 1950s, J.D. Robertson (Duke University) portrayed the plasma membrane as a three- layered structure, consisting of two darkly stained outer layers and a lightly stained middle layer using electron microscope. It was later demonstrated that the cell membranes contain a lipid bilayer. The two dark-staining layers correspond to the inner and outer polar surfaces. The light-staining layer is the hydrophobic fatty acid tails. All membranes, whether they are plasma, nuclear, or cytoplasmic membranes, or taken from plants, animals, or microorganisms, have this same ultrastructure.
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Overview of Membrane Functions 1. Compartmentalization 2. Scaffold for biochemical activities 3. Providing a selectively permeable barrier 4. Transporting solutes 5. Responding to external signals 6. Intercellular interactions 7. Energy transduction
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Compartmentalization At two levels: 1. Plasma membrane encloses the content of the entire cell, separating the cell from its surrounding environment. 2. Organelle and cytoplasmic membranes enclose diverse intracellular space, allowing specialized activities to proceed without external interference and to be regulated independently of one another.
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Scaffold for Biochemical Activities Synthesis of N-liked oligosaccharide in RER Membranes provide the cell with an extensive framework or scaffolding within which components can be ordered for effective interaction.
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Providing a Selectively Permeable Barrier Membranes prevent the unrestricted exchange of molecules from one side to the other, while promote the movement of select molecules into and out of the enclosed cellular compartment.
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Transporting Solutes Membranes contain the machinery for physical transporting substances from one side of the membrane to another, often from a region where the solute is present at low concentration into a region where that solute is present at much higher concentration.
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Responding to External Signals Membranes possess receptors that combine with specific molecules (or ligands) having a complementary structure. Different types of cells have membranes with different receptors and are, therefore, capable of recognizing and responding to different ligands in their environment.
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Intercellular Interaction The plasma membrane allows cells to recognize and signal one another, to adhere when appropriate, and to exchange materials and information.
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Energy Transduction Membrane are intimately involved
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