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difference betw facilitated diffusion & secondary active transport?

Discussion in 'MCAT Study Question Q&A' started by unsung, May 26, 2008.

  1. unsung

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    One place in the EK book suggests glucose transport into the cell is via facilitated diffusion. Another place suggests it is brought into the cell via secondary active transport. Which one is right?

    Also, if in active transport, ATP is used to "set up" a concentration gradient, does that mean the molecule is moving down its gradient after the ATP has been spent?

    Thanks!
     
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  3. rocuronium

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    Edit: This information is incorrect. See later posts for the correct information. -- Gleek

    I believe that neurons are the only cells that take up glucose by facilitated diffusion. All other cells take it up by active transport.

    When glucose is moved into the cell by active transport, it is still moving against its concentration gradient, but it is moving with the established concentration gradient.

    Does that make sense?
     
  4. tco

    tco
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    Like Gleek said, it depends on the concentration gradient.

    In the intestine, it requires energy because we're uptaking against the concentration gradient, transcytosing the glucose across the cell, and exocytosing out of the basal membrane.

    ATP is used to move molecules from areas of low concentration to areas of high concentration, this is against diffusion and the laws of thermodynamics, so energy must be spent.

    Hope that helps.
     
  5. koopa_troopa

    koopa_troopa Junior Member
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    Insulin causes the uptake of glucose into muscle, liver cells, etc by increasing the # of GLUT transporters. From what I remember, this is a passive process. So I don't think neurons are the only ones that take up glucose by facilitated diffusion.
     
  6. RySerr21

    RySerr21 i aint kinda hot Im sauna
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    gleek i think you are mistaken on this one. in almost all cells glucose is taken up by facilitated diffusion. thats the whole point of insulin...when insulin binds to its receptor, that stimulates GLUT4 transporters to work harder and also recruits more GLUT 4 transporters to come to the membrane from an intracellular pool of GLUT 4. i know there are trasnporters GLUT1-GLUT5 but in my course we only covered GLUT1 and GLUT 4 in major detail..either way, they all work by facilitated diffusion.

    i'm pretty sure the only time that glucose is transported across membranes via secondary active transport is when it is in the digestive system.
     
  7. G1SG2

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    Glucose is transported via secondary active transport ONLY in 1) the epithelial cells of the intestine and 2) the proximal tubule of the kidney. All other cells take up glucose via facilitated diffusion.
     
  8. rocuronium

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    Yup. You're right. I should have confirmed before posting.

    Thanks for pointing that out.
     
  9. tco

    tco
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    :p

    For the record, activating the glucose receptors is (I'm pretty sure) not a passive process. It almost certainly involves a G-Protein of some kind. Just about every signal receptor activates a G-protein it seems like...I'll look it up. If I post a retraction tomorrow, you'll know it's passive.
     
  10. RySerr21

    RySerr21 i aint kinda hot Im sauna
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    no problem. and dont worry... you'll always be a bad *ss with jack bauer as your avatar.

    i'm still pissed the last season never aired :mad:
     
  11. rocuronium

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    Me too! I was so choked. I really need a Jack Bauer fix...
     

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