Symporter

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A type of coupled transporter that simultaneously transfers a second solute in the same direction as the first. The tight coupling transfer of the two solutes allows the coupled transporters to obtain energy stored in the electrochemical gradient of the first solute to transfer the second one[1]. The free energy released during the 'downhill' movement of one solute is used to power the 'uphill' movement of the other solute in the same direction. These transporters will only transport both solutes at the same time, no one solute can be transported independantly[2].

Sodium is usually the co-transported ion that provides the driving force for transporting the second molecule. For example, the Na+ driven glucose symporter is commonly found in epithelial cells, where it obtains energy created by the Na+ electrochemical gradient. Glucose can then be transported against its concentration gradient into the cell, where it'll then passively diffuse out of the cell via the glucose uniporter into the extracellular fluid, from where it’ll diffuse into the bloodstream[3][4].

References

  1. Alberts,B., Johnson,A., Lewis,J., Raff,M., Roberts,K., Walter,P. (2008) 'Molecular Biology of The Cell' fifth ed., Garland Science, New York, pp.656
  2. Chander, N. and Viselli, S. (2010) Lippincott’s Cell and Molecular Biology, 1st edition, Lippincott Williams and Wilkins, chapter 14
  3. Alberts, B.A. and Johnson, A.J. and Lewis, J.L. and Raff, M.R. and Roberts, K.R. and Walter, P.W. 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. P656
  4. Alberts, B.A. and Johnson, A.J. and Lewis, J.L. and Raff, M.R. and Roberts, K.R. and Walter, P.W. 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. P659
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