notes2-1 - Membranes 16:20 Cells...

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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 
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 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
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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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