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The Cell as the Fundamental Unit of Life: Membrane Transport Processes

Explore the structure and functions of the cell membrane, including passive and active transport processes, facilitated diffusion, and membrane permeability factors. Learn about the roles of proteins and phospholipids in maintaining the cell's integrity.

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The Cell as the Fundamental Unit of Life: Membrane Transport Processes

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  1. The Cell as the Fundamental Unit of Life: Membrane Transport Processes

  2. Plasma Membrane Fluid mosaic model: • Working model of the membrane • Protein molecules bobbing in phospholipid sea • Proteins determine membrane’s specific functions

  3. Structure of Cell Membrane Phospholipids • Most abundant lipid • Polar/hydrophilic head(attracted to water) • Pair of nonpolar/hydrophobic tails(repelled by water) Hydrophilic head Hydrophobic tails

  4. Phospholipid

  5. Phospholipid Bilayer Polar heads, outside & inside Nonpolar tails in the interior cell membranes outside Hydrophilic head phospholipid Hydrophobic tail Hydrophilic head inside

  6. Specializations of the Plasma Membrane Microvilli- intestinal cells Membrane Junctions Tight junctions Desmosomes Gap junctions

  7. Plasma Membrane Function Selectively permeable- allows certain substances to pass through By 2 ways: active or passive transport Passive- downhill Active- uphill (needs energy)

  8. Passive & Active Transport Passive: downhill reaction • Simple diffusion • Osmosis • Facilitated diffusion • Filtration Active: uphill reaction, needs ATP • Exocytosis • Endocytosis - Pinocytosis - Phagocytosis

  9. Passive Diffusion • No Barrier: • Substances “spread out” • High concentration to low concentration e.g.: Blue dye placed in flask of water Reached equilibrium Pure water Blue dye

  10. Passive Diffusion Biological membrane: • Substances diffuse • High concentration to low concentration • Pores in membrane must be large • “Down the concentration gradient” • Dynamic equilibrium, equal rates in both directions

  11. Facilitated Diffusion • Carrier proteins: • Bind specific molecule & change shape • Pass molecule through middle of protein

  12. Passive Diffusion • Osmosis- diffusion of a water through a semi-permeable membrane • Moves down concentration gradient e.g., Two sugar solutions of different concentrations separated by porous membrane which lets water through but not sugar What will happen?

  13. Passive Diffusion: Terms & Osmosis • More concentrated to less concentrated • Until concentration same on both sides: isotonic

  14. Passive Diffusion: Terms & Osmosis Concentration of solute less: solution is hypotonic. Concentration of solute greater: solution is hypertonic.

  15. Passive Diffusion: Outcomes to Living Animal Cells Animal cells No cell walls Isotonic environment: Influx of water equals the efflux of water No change in cell shape

  16. Hypotonic solution: Water enters cell Bursts, or lyses Passive Diffusion: Outcomes to Living Animal Cells Hypertonic solution: Water leaves cell Shriveled, or crenate

  17. Passive Transport: Filtration Glomerular filtration

  18. Passive Transport and Facilitated Diffusion ATP • Passive transport & facilitated diffusion do NOT require

  19. Active Transport ATP DOES require the input of outside cell • Transport proteins AGAINST concentration gradient inside cell

  20. ATP

  21. Role of ATP in Energy Metabolism ATP  ADP + Pi + Energy

  22. Endocytosis

  23. Exocytosis

  24. Secretion

  25. Exocytosis mucus Goblet cell http://www.1lecture.com/Physiology/Endocytosis%20and%20Exocytosis/index.html

  26. Membrane Permeability 1 2 3 4 • Cell membrane: • selectively permeable • 4 factors that determine permeability lipid solubility • molecular size • polarity • charge

  27. Lipid solubility • Most important factor • Hydrophobic molecules Passively diffuse Hydrocarbons, carbon dioxide, & oxygen

  28. Molecular Size and Polarity - + Molecular Size Larger molecules, less permeable Lower kinetic energy Small pore sizes in the membrane Polarity Polar molecules hydrophilic, less permeable Very small, polar uncharged (water) molecules can diffuse

  29. Charge • Charged molecules hydrophilic, less permeable Surrounded by coat of water (hydration shell), increases the size

  30. INQUIRY • What is the main difference between active transport and facilitate diffusion? • In osmosis, water moves from a xxxx solution to a xxxx solution. • What happens to blood cells placed in pure water? • Which portion of the phospholipid molecule faces the environment outside of the cell? • The release of insulin from certain human cells is an example of xxxx(endo, exo, phago, pinocytosis).

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