Symporters

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A symporter is one of two types of coupled transporters that are used in active transport. It moves molecules through the phospholipid bilayer against their concentration gradient (energetically unfavourable reaction) by harnessing the energy released from a second molecule that is being transported down its concentration gradient (energetically favourable reaction) at the same time. Molecules want to move from a high to a low concentration so if the molecule is moving from a low to a high concentration (against its gradient) it requires energy to so do therefore simple diffusion or facilitated diffusion cannot be used as they are forms of passive transport. Instead, either a coupled transporter or a uniporter can be used. The second type of coupled transporter is an antiporter which transports the two molecules in opposite directions. Symporters transport the target molecule (that needs to be moved) and the molecule the energy is being taken from are moving in the same direction[1]. An example of a symporter is moving glucose up its concentration gradient (often referred to as uphill movement) by using the energy from the movement of sodium ions that are moving down their gradient (downhill movement)[2].

All of these types of transporter are types of carrier protein and use energy by hydrolysing ATP to ADP and a phosphate[3].

References

  1. •B. Alberts et. al (2008) Molecular Biology of The Cell, 5th Edition, New York: Garland Science (pg 656)
  2. •B. Alberts et. al (2008) Molecular Biology of The Cell, 5th Edition, New York: Garland Science (pg 657)
  3. •B. Alberts et. al (2008) Molecular Biology of The Cell, 5th Edition, New York: Garland Science (pg G:37)
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