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CELL MEMBRANES

CELL MEMBRANES. The Fluid-Mosaic Model. This is an introduction to the structure and function of cell membranes. It is designed to be a self-contained unit with links to other, related material. THE FUNCTION OF CELL MEMBRANES. Compartmentalization of tissues Regulation of cell contents

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CELL MEMBRANES

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  1. CELL MEMBRANES • The Fluid-Mosaic Model This is an introduction to the structure and function of cell membranes. It is designed to be a self-contained unit with linksto other, related material.

  2. THE FUNCTION OF CELL MEMBRANES • Compartmentalization of tissues • Regulation of cell contents • Provides surface for enzymes, receptors, recognition, etc. It is thought by some that the spontaneous organization of membranes played an important role in the evolution of life.

  3. PHOSPHOLIPIDS: The “Backbone” of the Membrane Cartoon of a phospholipid molecule This cartoon depicts the basic amphipathic* structure common to all phospholipids Glycerol plus polar side group Fatty acids * both polar and non-polar regions

  4. WATER MOLECULES ARE POLAR • Structure of water and the Cartoon version • Water is a dipole d/2 + H d + O d/2 + H Oxygen pulls electrons towards itself causing a charge imballance (d-)

  5. - Cl + Na - + - + - + - + - + - + Water is a good solvent for polar molecules and ions - + Hydration Shells - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - +

  6. PHOSPHOLIPIDS • Cartoon of a phospholipid molecule Non-polar tail (Hydrophobic- hates water) Polar head (Hydrophilic- likes water)

  7. OIL WAIT OIL/WATER PARTITION: THE “KITCHEN” EXPERIMENT MIX OIL WATER AND TEST SUBSTANCE CONCENTRATION OF TEST SUBSTANCE IN OIL/ CONCENTRATION OF TEST SUBSTANCE IN WATER = OIL WATER PARTITION COEFFICIENT (OWPC=K) K > 1 HYDROPHOBIC (NON-POLAR) K < 1 HYDROPHILIC (POLAR) WATER

  8. MIXING PHOSPHOLIPIDS AND WATER: Spontaneous Self-Organization Click to next slide to see the spontaneous self-organization

  9. MIXING PHOSPHOLIPIDS AND WATER: Spontaneous Self-Organization Click ahead

  10. MIXING PHOSPHOLIPIDS AND WATER: Spontaneous Self-Organization Click ahead

  11. MIXING PHOSPHOLIPIDS AND WATER: Spontaneous Self-Organization

  12. Phospholipids plus water make a self-organizing system • Low lipid/water ratio - micelles • High lipid/water ratio - lamellae • Single lamellae = bilayer or sheet

  13. Sheet Micelle

  14. The Black Lipid Membrane (BLM) • Formed across a small hole in a teflon beaker using a sable artist’s brush • Viewed with an optical system • Looks like a soap bubble with large patches of black where the bilayer forms • Used as a laboratory model of the cell membrane

  15. The Black Lipid Membrane (BLM) • Experimental Setup Microscope Outer Beaker Inner Beaker What you see Light Source

  16. Permeability of the BLMmol/sec-sq. cm.

  17. The Black Lipid Membrane Could be used to Show what else is in Cell Membranes • It has too low permeability for ions- it needs protein and polypeptide to help them get through (channels and carriers) • It needs cholesterol for proper “fluidity” • It needs carbohydrate to provides cell recogtnition properties

  18. The membrane is fluid

  19. The membrane is fluid

  20. The membrane is fluid

  21. The membrane is fluid

  22. Cholesterol sits between fatty tails

  23. Proteins can span the bilayer Hydrophilic Hydrophobic

  24. The fluid-mosaic model • Lipid bilayer • Cholesterol between tails • Protein, Glycoprotein, Lipoprotein “dissolved” in the lipid portion

  25. The fluid-mosaic model

  26. Channels and carriers are needed to get ions across the bilayer

  27. Channels and carriers are needed to get ions across the bilayer

  28. Cell Membranes Become Network Elements in Tissue Membranes • Epithelia are tissue membranes made up of cells • Network Thermodynamics provides a way of modeling these composite membranes • Often more than one flow goes through the tissue

  29. An Epithelial Membrane in Cartoon Form:

  30. A Network Model of Coupled Salt and Volume Flow Through an Epithelium CL PL LUMEN AM TJ BL CELL BM BLOOD PB CB

  31. What to do now? • Please contact me to tell me what your reaction to the presentation is. • If you wish to see how well you understood the presentation, try the SELF TEST.

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