cell1-membranes-reading - 1 Biology 326 -General Physiology...

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Unformatted text preview: 1 Biology 326 -General Physiology Membrane transport: simple diffusion, ion channels, GLUTs, pumps, regulation of pH and volume. January 11-15th, 2010 Dr. M. Sweeney-Nixon Objectives. At the end of this lesson, you will be able to describe passive transport (diffusion) and active transport processes across the plasma membrane and their role in regulation of cell pH and volume. Also, you will be able to describe why cells regulate pH and volume by stating reasons that they change, and their importance to cell homeostasis. The structure of cellular membranes is referred to as the fluid mosaic . Membranes consist primarily of lipids ( fluid ) and proteins ( mosaic ), with carbohydrates to a much lesser extent. Phospholipids form the lipid bilayer - 3 common phospholipids are phosphatidyl-choline, phosphatidyl- ethanolamine & phosphatidyl-serine. (These have choline, ethanolamine or serine groups on the phosphate group of the lipid). Common saturated fatty acids are palmitate (c16) and stearate (c18); unsaturated fatty acids are oleate (c18, 1 dbl bd) & linoleate (c18, 2dbl bds). Other lipids in animal cell membranes are sphingolipids and cholesterol. Other lipids in plant cells include glycolipids (lipids containing an oligosaccharide). Membranes... 1. ... define boundaries of cells, and serve as a permeability barrier. Lipids form a physical barrier to hydrophilic substances ( ) i.e. isolate the cell and its parts. 2. ... define compartments in cells: e.g. nucleus, mitochondrion, ER, Golgi, chloroplasts, vacuoles, vesicles. This organizes a cell and segregates specific functions. 3. ... regulate movement of substances in and out of cells: facilitated diffusion and active transport occurs at membranes on specific membrane proteins called transporters. Thus, proteins control entry & exit of ions and nutrients. 4. ... detect and transmit signals such as hydrophilic hormones and neurotransmitters: this is called signal transduction. Thus, protein receptors & enzymes allow cell signals to be received. Receptors control transporters as well. 5. ... communicate with other cells by direct cell contact (gap junctions). Proteins maintain shape by joining cell membranes to the extracellular matrix (ECM) and maintain cell shape by connecting to the cytoskeleton. 2 Membrane proteins . Plasma membranes transport materials between the cell and its environment. Such transport is Passive or Active no expenditure of cellular energy Requires energy expenditure from the cell (uses the kinetic energy of molecular movement) (uses ATP directly or indirectly in Na+ gradients). diffusion down concentration or transports against gradients on protein electrochemical gradients pumps e.g. Na + K + ATPase Table 1. Forms of transport across membranes and compounds transported Passive transport = diffusion from high to low concentrations Active transport against natural gradients....
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cell1-membranes-reading - 1 Biology 326 -General Physiology...

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