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Chapter 5

Chapter 5. Cell Transport. Fluid Mosaic Model. Regulates how cellular molecular traffic Small molecules and ions move across plasma membrane in both directions Sugars, amino acids, nutrients enter cell Waste, carbon dioxide leave the cell Selectively permeable Exclude some molecules

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Chapter 5

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  1. Chapter 5 Cell Transport

  2. Fluid Mosaic Model • Regulates how cellular molecular traffic • Small molecules and ions move across plasma membrane in both directions • Sugars, amino acids, nutrients enter cell • Waste, carbon dioxide leave the cell • Selectively permeable • Exclude some molecules • Regulate rate of movement of substances

  3. Permability of membrane • Hydrophobic molecules • Hydrocarbons, oxygen and carbon dioxide • Dissolve in lipid bilayer and pass through easily • Hydrophilic molecules • Water, ions, glucose, polar molecules • Movement impeded by hydrophobic core of lipid bilayer • Transport proteins • Channel for passage of hydrophilic molecules • Physical transport of specific substances

  4. Kinds of transport through the membrane: Passive Transport Simple diffusion Osmosis Facilitated diffusion Active Transport Vesicle-mediated transport

  5. Concentration Gradient • The type of transport depends on the concentration gradient: • Passive transport

  6. Diffusion • Tendency for molecules of a substance to spread out into the available space • Each molecule moves randomly (kinetic movement) • Population of molecules moves directionally • Down concentration gradient • Until equilibrium is reached • Examples: dye, perfume

  7. Concentration gradients • Substances naturally move without energy down their concentration gradient • Each substance is unaffected by the other substances • Substances will diffuse across membranes from areas of high concentration to areas of low concentration • If membrane is permeable to the substance • Passive transports • Occur without input of cellular energy • Regulated by concentration gradients and membrane permeability

  8. Simple diffusion

  9. Osmosis • Passive transport of water across a selectively permeable membrane • Rapid osmosis facilitated by aquaporins • Regulated by • Solute concentration • Osmotic pressure

  10. Osmosis

  11. Osmosis: An Example

  12. Solute concentration • Relative terms • Only useful when comparing different solutions • Hypertonic • Solution with a higher concentration of solutes • Lower water concentration • Hypotonic • Solution with a lower concentration of solutes • Higher water concentration • Isotonic • Solutions have an equal concentration of solutes • Equal water concentrations

  13. Solute concentrations • Water moves from hypotonic to hypertonic solutions • Down concentration gradient • Until equilibrium is achieved • Kind of solutes doesn’t matter only total concentration • Isotonic solution have random movement of molecules, no net movement

  14. Osmosis In Animal Cells

  15. Osmoregulation • Control of water balance in living systems • Most organisms are isotonic to their environment • Seawater is isotonic to most marine invertebrates • Terrestrial animals have isotonic ECM • Special adaptations for organisms not in isotonic environments • Cell membranes that regulate influx of water • Contractile vacuole • Organisms with cell wall • Cell wall prevents bursting • Exerts pressure back, counteracting solute pressure • Plasmolysis if cell is hypertonic

  16. Osmosis In Plant Cells Hypotonic Isotonic Hypertonic Turgid Flaccid (normal) Plasmolyzed

  17. Facilitated diffusion

  18. Facilitated diffusion • Down concentration gradient=diffusion • Means of carrier protein • Like an enzyme • Solute specific=specific binding site • Transport proteins can get saturated • Can be inhibited • Catalyze a physical process • Hydrophilic channels • Aquaporins • Gated channels • Stimulus cause them to open or close • Chemical (neurotransmitters) • Electrical • Transport proteins • Undergo changes in shape to bind and translocate solutes across membrane • Triggered by binding and release of transported molecule

  19. Facilitated diffusion in action

  20. Failure of transport systems • Cystinuria • Absence of protein that transports cysteine across membranes of kidney cells • Develop stones from amino acid accumulation in kidneys

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