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Cellular Transport and Tonicity

Cellular Transport and Tonicity. Biology 2121. Selective Permeability of the Plasma Membrane. Which substances can move freely through the phospholipid bilayer ? Water, gases (oxygen, carbon dioxide); fats Small- polar; nonpolar molecules Which substances are blocked ?

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Cellular Transport and Tonicity

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  1. Cellular Transport and Tonicity Biology 2121

  2. Selective Permeability of the Plasma Membrane • Which substances can move freely through the phospholipidbilayer? • Water, gases (oxygen, carbon dioxide); fats • Small- polar; nonpolar molecules • Which substances are blocked? • Glucose; ions • Larger substances (polar) • Processes • Passive (no ATP) • High to lower concentration gradients • Driving Force? KE of the substances • Active (requires ATP) • Low to higher concentration gradients

  3. Passive Processes • 1. Diffusion vs. Osmosis • 2. SimpleDiffusion • Gases; nonpolar; lipid soluble substances (fat-soluble vitamins) • 3. FacilitatedDiffusion • Sugars (glucose; amino acids; ions) • Integral or Transmembrane proteins • Channel or carrier proteins • 4. Osmosis • Movement of water dependent on solute concentration (extracellular/intracellular)

  4. Tonicity • Measure of the ability of a solution to cause a change in cell shape or tone caused by osmotic flow of water • Why does osmosis occur? • Water concentration differences • Soluteconcentration affects water concentration • Dependent on the number (concentration) • Osmolarity • Permeability of solutemolecules • Permeable to all solute molecules – equilibrium • If membrane is impermeable (see U-tube)

  5. Water Movement and Solute Concentration

  6. Tonicity – Conditions • Isotonic • Cells have same concentrations of non-penetrating solutes as found in cells • Our cellular fluids and IV’s • Hypertonic • Solutions have higher concentration of non-penetrating solutes • Salty or high saline conditions • Hypotonic • Solutions containing a lower concentration of non-penetrating solutes • “dilute”

  7. Active Transport • Driving Force? ATP • Solute “pumps” (ions- K+, Na+, etc.) • Sodium-PotassiumPump • “primary active transport” • Neurons, cardiac and skeletal tissue • VesicularTransport • Fluids contain large particles and macromolecules • Vesicles

  8. Vesicular Transport • Exocytosis • “ejects” substances from cells • Hormone and mucous secretion • Endocytosis • Substance moves into cell and vesicle formed • transcytosis, vesicular trafficking • Phagocytosis • Pinocytosis

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