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notes2-1 - Membranes 16:20 Cells The minimum organization...

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Unformatted text preview: Membranes 16:20 Cells The minimum organization of living matter. CELL MEMBRANE MODELS (plasma membrane): All cells have a thin outer covering. Plasma membrane or cell membrane Early models of cell membranes inferred that structure from chemical and permeability properties of the membrane Fluid-Mosaic Model (fig 7.7, 7.4) 2 layers of phospholipids as before, but now exposed proteins in a mosaic patterns, not a continuous layer pores bounded by protein as before fluidity: proteins and phospholipids can move (dynamic structure), evidence from hybrid cells Cell Coats: (not a separate entity from the cell membrane) Composition o glycolipids, glycoproteins Function o Cell recognition Why do membranes exist ? structural Functional properties: o maintain concentrations of molecules and ions o create free energy gradients o orient molecules into functional complexes Osmosis net movement of water across a semi-permeable membrane o (ie permeable to water, but not solutes) Terminology of Solutions Relative to one another: (fig 7.13) Hypertonic: more concentrated Isotonic: equal concentration Hypotonic: less concentrated Example: A single celled freshwater organism, such as paramecium, is transferred to saltwater. Which of the following is likely to happen? The cell shrinks Water will ________ the cells of a fish living in fresh water because of the process of osmosis. What is the relationship between the cytoplasm of the cells that line the passageway of the lungs and the extracellular fluid? Normally-cytoplasm is hypotonic Cystic fibrosis- cytoplasm is hypertonic Factors involved in the permeability size and shape of molecules solubility in lipids net electric charge chemical properties ------But water moves freely across the membrane------ important to study the movement of water water is the universal solvent in biological systems Movement of Substances Across Membranes: Many substances can move by diffusion, since the membrane is permeable to them (simple sugars, amino acids, lipids) o Small molecules o Lipid soluble molecules Permeases: molecules that are not permeable or that move slowly o large molecules o charged molecules o permeases are membrane bound proteins that facilitate the movement of molecules across the membrane. Categorized by energy use Diffusion: Movement of small molecules as a consequence of thermal agitation (thermal energy) (fig 7.11)...
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notes2-1 - Membranes 16:20 Cells The minimum organization...

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