Chapter 5

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

18. Facilitated diffusion

19. 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

20. Facilitated diffusion in action

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