Active Transport

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Active transport is the process in which certain molecules or ions are pumped across a membrane via transmembrane proteins, against their concentration gradient[1]. For this mechanism to work, and source of free energy must be supplied so the solute can move from an area of low concentration to an area of high concentration[2]. This source of energy can either come from the hydrolysis of an adenosine triphodphate (ATP) molecule or an existing ion gradient[3].

There are two types of active transport. There are both primary and secondary active transport. Primary active transport is where two different molecules move across a membrane whilst using the energy released from when ATP is hydrolysed. The molecule enters one of the many transmembrane proteins and ATP binds to it. This ATP is then hydrolysed causing the tranmembrane protein to be phosphorylated. This results in the protein chnaging shape to allow the molecule to be released on to the other side of the membrane[4]. Secondary active tranpsort is the co-transportation of one molecule by another. The movement of one molecule produces potential energy whilst it moves down its concentration gradient and this potential energy is used to drive the other molecule against its concentration gradient. Molecules can either move in the same direction or in opposite direction with secondary active transport. When they move in the same direction this is known as a symporter. When they move in opposite directions, this is known as an antiporter[5].

References

  1. Alberts, B et.al. (2008). Molecular Biology of the Cell. 5th Edition. New York: Garland Science, Taylor and Francis Group, LLC. Page 654.
  2. Berg, J et.al. (2012). Biochemistry. 7th Edition. United States of America: W.H. Freeman and Company. Page 385.
  3. Alberts, B et.al. (2008). Molecular Biology of the Cell. 5th Edition. New York: Garland Science, Taylor and Francis Group, LLC. Page 654.
  4. Berg J, Tymoczko J, Stryer L. (2007) Biochemistry, Sixth edition, New York: WH Freema
  5. Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K. and Walter, P. (2008) Molecular biology of the cell, 5th edition, Garland science.

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