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Cell membranes

  1. Oct 28, 2004 #1
    Hi. What prevents proteins from falling out of cell membranes?

    This question has been bothering me for sometime.... and I cannot find an answer to this. Please help :tongue2:
  2. jcsd
  3. Oct 28, 2004 #2
    Most proteins within the cell are suspended (floating around) in the cytosol (liquid within the cell), those on the outside are physically attached (either covalently bonded or via hydrophobic interactions) to the cell membrane.
  4. Oct 28, 2004 #3
    Proteins can be found in numerous places in the cell. Let's begin with the phospholipid bilayer. These proteins can exist within the cell membrane which are known as integral memebrane proteins, or they can be hydophylic proteins which exist as preriferial membrane proteins which interact with other proteins. The proteins within the cell do not fall out of the cell because of the cell membrane. Cell membranes that only allow certain things to pass through are said to be selectively permeable. Proteins, because of their size go in and out of the cell through what is known as exo and endo cytosis. Unlike other molecues and substances that diffuse either through the membrane itself or by active transport, these protiens exit the cell through exo cytosis. But not any protein leaves. Depending on what type of R group is attached to the polymer, usually a polypeptide, also depends on the destination of the cell. These R groups are attached to the protein in the ER and then sent to the Golgi for shipping. Hope that helped.
  5. Oct 29, 2004 #4
    thanks people. But what exactly makes cell membranes selectively permeable (yes i know, this sounds silly)?
  6. Oct 29, 2004 #5
    i think its the hydrophyillic and hydrophobic ends of the protiens that are so close together, that only certain things can pass through.
  7. Oct 29, 2004 #6
    I think proteins are selective, they form gates for things they know only. they do not let others they don't recognize. for example, there are membrane proteins for glucose, for ions. What's not recognized is not let in out out. That makes selective permeability.

    proteins don't fall through the membrane because they are attached at the membrane with their transmebrane parts that are hydrophobic, or with other interactions.
  8. Oct 29, 2004 #7
    As said by Noticibly F.A.T. it is the hydrophyllic and hydrophobic ends however its not of the proteins. What makes up the phospholipid bilayer is the lipid known as phospholipid. Basically it is a triglyceride, containing a glyercol (hydroxyl group) and three fatty acids (carboxyl groups) The only difference in a phospholipid is that one of the fatty acids is replaced with a phosphate group. The name of the lipid is no coincidence. It is the arrangement of these phospholipids that only allow smaller particles that match the properities of the bilayer to pass through. However Noticibly F.A.T. is correct if they are talking about channel proteins (integral membrane proteins) which, as they said, contain hydrophobic and hydrophillic regions. However what makes the membrane selectively permeable is not the proteins but the phospholipids and their characteristics. :wink:
  9. Oct 31, 2004 #8
    Yeah, i meant the channel membranes, but you cleared up my answer. Thanks man.
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