Ch+5++Biological+Membranes - Biological Membranes Chapter 5...

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Biological Membranes Chapter 5 Plasma Membrane 1. Physically separates interior of cell from external environment 2. Receives information about changes in environment 3. Regulates passage of materials in and out of cell 4. Communicates with other cells 5. Forms compartments to allow separate functions 6. Participates in biochemical reactions Fig 5-2: Fluid Mosaic Model : According to the fluid mosaic model, cell membranes consist of a fluid bilayer composed of phospholipids in which a variety of proteins are embedded Fig 5-4: The Lipid Bilayer: Fluid or liquid-crystalline state. Proteins move within the membrane. Flexible and self-sealing. Capable of fusing with other membranes. Allows transport of materials within cell. Forms vesicles - bud from one cell membrane; fuse with another membrane to facilitate movement of materials from one part of the cell to another. Proper membrane function in fluctuating temperature: Low temp, motion of FA chains slowed. Membrane becomes semi solid; transport ceases if too rigid Component lipids important – Double bonds cause kinks in FA chains and prevent hydrocarbon chains from interacting through Van der Waals forces. More fluid. Unsaturated fats therefore lower the temperature at which membrane lipids solidify Fig 5-6: The Plasma Membrane A: Integral membrane proteins embedded in bilayer (not easily removed), amphipathic; hydrophilic heads extend into cytoplasm, hydrophobic regions interact with FA tails of membrane phospholipids B: Peripheral membrane proteins at inner or outer surface of bilayer Fig 5-7: Membrane Proteins and Fig 5-9: Membrane Protein Synthesis Membrane Proteins: Transport materials . Act as enzymes or receptors. Recognize cells. Structurally link cells Fig 5-10: Anchoring; Fig 5-10: Passive Transport; Fig 5-10: Active Transport; Fig 5-10: Enzymatic activity; Fig 5-10: signal transduction; Fig 5-10: cell recognition; Fig 5-10: intercellular junction Membrane proteins, and thus membranes, have many functions: transport of materials, enzymatic activity, transmission of information and recognition of other cells Selectively Permeable Membranes: Allow passage of some substances but not others. Most permeable to nonpolar molecules (that can pass through lipid bilayer). Relatively impermeable to ions and large polar
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Ch+5++Biological+Membranes - Biological Membranes Chapter 5...

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