Membrane structure and function
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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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  • 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)







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



Pass through membrane easily
Pass through Membrane Easilyhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/MembraneProteins.gif

  • 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.






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





  • Movement of H other.2O across selectively permeable membrane - osmosis.






In this case, the protein actually rotates ] gradient with help of transport protein.

to dump the materials to the inside

of the cell.







More active transport
More Active Transport (Na

  • 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.



  • 1 (NaPhagocytosis (“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.


  • 2 (NaPinocytosis (cell drinking) - cell creates vesicle around droplet of extracellular fluid.


  • 3 (NaReceptor-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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