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Membrane Structure and Function

Membrane Structure and Function. Chapter 7. Plasma membrane of cell selectively permeable ( allows some substances to cross more easily than others) Made mostly of proteins and lipids (phospholipids). Phospholipids and proteins create unique physical environment (fluid mosaic model).

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Membrane Structure and Function

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  1. Membrane Structure and Function Chapter 7

  2. Plasma membrane of cell selectivelypermeable (allows some substances to cross more easily than others) • Made mostly of proteins and lipids (phospholipids). • Phospholipids and proteins create unique physical environment (fluid mosaic model)

  3. Phospholipid

  4. Membrane - bilayer - hydrophilic (water loving) heads pointing outwards, hydrophobic (water fearing) tails pointing inwards. • Proteins help membrane to stick to water.

  5. Fluid because lipids and proteins can move laterally. • As temperatures drop, liquid membrane can solidify.

  6. Cholesterol found in membrane helps with fluidity of membrane. • Membranes need to be fluid to work properly.

  7. Two different types of proteins are found in membrane. • 1Peripheral proteins not in membrane, bound to surface of protein. • 2Integral proteins in membrane often spanning entire membrane.

  8. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/MembraneProteins.gifhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/MembraneProteins.gif

  9. Also aids in cell-to-cell recognition (ability of a cell to distinguish one type of neighboring cell from another)

  10. Pass through Membrane Easily • Some substances move steadily across membrane (sugars, ions, and wastes like CO2) • Hydrophobic molecules (i.e. hydrocarbons, CO2, and O2) can dissolve in lipid bilayer and cross easily.

  11. Charged particles and polar molecules have more difficulty passing.

  12. Diffusion - tendency for substance to spread out in open area. • Move from an area of Most concentrated to Least concentrated.

  13. No force acting upon it - substance will tend to move down it’s concentration gradient (passive transport).

  14. Diffusion of molecules with limited permeability through lipid bilayer may be assisted by transport proteins.

  15. http://library.thinkquest.org/27819/media/protein_channel.gifhttp://library.thinkquest.org/27819/media/protein_channel.gif

  16. Difference in concentration - ions move from one area to other. • Solution with higher [ ] solutes - hypertonic. (water moves out) • Solution with lower [ ] solutes -hypotonic. (water moves in) • [ ] equal - isotonic.

  17. http://www.biologycorner.com/resources/hypertonic.gif

  18. http://www.biologycorner.com/resources/hypotonic.gif

  19. Movement of H2O across selectively permeable membrane - osmosis.

  20. Organism does not have rigid walls must have ability to osmoregulate and maintain internal environment. • Allows plant to stand up against gravity (turgid cell); not watered, plant will begin to wilt (flaccid cell).

  21. Plant loses enough water, plasma membrane will pull away from cell (plasmolysis).

  22. http://faculty.southwest.tn.edu/jiwilliams/plasmolysis.gif

  23. facilitated diffusion - diffusion of substance down it’s [ ] gradient with help of transport protein. • Some channel proteins (gated channels) open/close depending on presence/absence of physical or chemical stimulus.

  24. In this case, the protein actually rotates to dump the materials to the inside of the cell.

  25. Active transport- materials need to be moved against [ ] gradient • Requires energy of cell to move substances from an area of low [ ] to an area of high [ ] (i.e. sodium-potassium pump in animal cells)

  26. http://www.sp.uconn.edu/~terry/images/anim/antiport.gif

  27. Sodium-potassium pump actively maintains gradient of sodium (Na+) and potassium ions (K+) across membrane. • Sodium-potassium pump uses energy of 1 ATP to pump 3 Na+ ions out and 2 K+ ions in.

  28. http://bioweb.wku.edu/courses/Biol131/images/neuronions.GIF

  29. Some organisms have proton pumps that actively pump H+ out of cell (i.e. plants, bacteria, and fungi)

  30. More Active Transport • Exocytosis - When membranes meet - fuse - material is let out to outside of cell. • Endocytosis - Membrane is inwardly pinched off and vesicle carries material to inside of cell.

  31. http://www.kscience.co.uk/as/module1/pictures/endoexo.jpg

  32. 1Phagocytosis (“cell eating”) - cell engulfs particle by extending pseudopodia around it, packaging it in a large vacuole. • Contents of vacuole are digested when vacuole fuses with lysosome.

  33. 2Pinocytosis (cell drinking) - cell creates vesicle around droplet of extracellular fluid.

  34. 3Receptor-mediated endocytosis - specific in transported substances. • Extracellular materials bind ligands (receptors) - causes vesicle to form. • Allows materials to be engulfed in bulk (i.e. cholesterol in humans)

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