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Cotransport: need help understanding it

  1. Sep 14, 2010 #1
    i am reading campbell right now and i seem to be having a brain fart as i cannot understand what a cotransport is. I am reading the words but my brain is not working. So can i get some help here?

    What is it in terms of its function, how it works, etc.

    thank you
     
  2. jcsd
  3. Sep 14, 2010 #2

    Ygggdrasil

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    Active transport, moving substances from an area of low concentration to high concentration, requires a sources of energy. This process is important for cells to uptake nutrients like glucose. Even if there is a lower concentration of glucose outside of the cell than inside of the cell, the cell still wants to take up glucose from its environment in order to fuel processes inside the cell.

    One way to perform active transport to uptake nutrients like glucose is to power active transport with ATP. Another way is to power active transport is to link the unfavorable transport of one molecule to the favorable transport of another. Just as you can extract energy from water flowing downhill, you can extract energy from a molecule going down its concentration gradient (going from a region of high concentration to low concentration). For example, the concentration of sodium outside the cell is higher than the concentration of sodium inside of the cell. Therefore, you can extract energy from the flow of sodium into the cell. Sodium-glucose transporters do just this; they link the favorable transport of sodium into the cell to the unfavorable transport of glucose into the cell.

    Perhaps here's a useful analogy. Frat parties usually have a lot of guys and few girls. Therefore, a guy who wants to get into the party will probably be turned away as the party already has too many guys. However, if this guy shows up to the party with a girl (or two), the frat boys are much more likely to let him and his friends into the party just so that the party will have more girls. Here, much like in the case of sodium-glucose cotransport, the guy achieves entry into the frat party by linking his entry to the favorable import of girls into the frat house.
     
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