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Lecture 1 - Transport Methods

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Michelle French

PSL300 Lecture 1 important for cell identification (ex. immune responses), cell adhesion Cell membrane Membrane Fluidity Membrane Permeability Depends on: Determined by lipid composition molec size Essential for working protein carriers and channels (allowing shape lipid solubility (2x. H 0-soluble molec cant pass) changes for function) Reduced by aging and poor diet charge ex. Cholesterol leaky lets things thru Membrane = permeable to a substance if the substance can cross by any means ex. Lack of unsaturated fats ex. Wrong proportion of amino+fatty acids in membrane Permeable to: Gases Cholesterol: stabilizes membrane Lipid-soluble molec (ex. Fat) so diffuse thru readily prevents diffusion of polar molecules across it Impermeable (wont let thru) to: Membrane Proteins (embedded) organic anions structural support for anchoring to cytoskeleton in cell interior large molec stabilization prots Receptors for signaling molec in metabolic processes anything strongly polarized ex2 H 0 Enzymesion pumps for active transport need prot Channels or Carriers to cross Membrane-Spanning Proteins: Cross membrane multiple times (most commonly 6 or 7) Structure Fluid-Mosaic Model Phospholipid Bilayer Helical embedded portions polar head (inner+outer surface): Loops on outer surfaces often attached to carb chains (glycocalyx) glycerol NH 2t one end, COOH at the other phosphate (hydrophilic) cholineserine or other amino acids nonpolar (interior): 2 long fatty acid chains (hydrophobic) 1 = saturated: straight 1 = polyunsaturated: [email protected] determines membrane properties cholesterol embedded btwn the chains splits into layers in freeze fracture electron microscopy Glycocalyx: Matrix of long carbohydrate filaments fuzzy external surface Fill extracellular space btwn cells slowing diffusion Anchored to membrane glycolipids + glycoproteins glyco- as prefix since anchored to glycocalyx Transmembrane Channels For diffusion of select molecions often contain hyaluronic acid, chondroitin sulfate2+ 4-5 prot subunits fit snuggly together net (-)ve charge polarized sequestersattracts Ca central pore created thru membrane
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