Active transport

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Active transport is the movement of the molecules against their concentration gradient using Adenosine triphosphate (ATP) as a source of energy. The molecules move through transmembrane proteins which act as pumps[1]. There are two types of active transport; primary active transport and secondary active transport. Primary active transport is the movement of two different molecules using the energy released from the hydrolysis of ATP. It is usually called ATPase; an example of primary active transport is Na+/K+ ATPase, this is responsible for about 30% of the overall ATP consumption of the body. As the molecule enters the membrane protein, ATP binds and is hydrolysed causing phosphorylation of the protein. The phosphorylation produces a conformational change of the protein so the molecule is released on the other side of the membrane[2]. Secondary active transport is the co transportation of one molecule by the other; the potential energy produced by the movement of molecule down its concentration gradient is used to drive the movement of another molecule against its concentration gradient. The two molecules can be transported in the same direction across the membrane such as with Na+ - glucose, this is known as a symporter. Molecules can also be transported in different directions across the membrane, as one moves into the cell the other moves out, this occurs in the movement of the Na+ - Ca2+ exchanger and is known as an antiporter . An example of secondary active transport is Na+ - Ca2+ exchanger  for intracellular Ca2+ homeostasis[3].

Active transport is an excellent example of a process whereas cells require energy, or ATP in this case. Active transport is very important as it allows the cell to uptake essential molecules such as glucose even when they are at low concentrations outside the cell.

References 

  1. Berg J, Tymoczko J, Stryer L. (2007) Biochemistry, Sixth edition, New York: WH Freeman
  2. Berg J, Tymoczko J, Stryer L. (2007) Biochemistry, Sixth edition, New York: WH Freeman
  3. 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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