Secondary active transport

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Secondary active transport is a type of active transport that moves two different molecules across a transport membrane. One of the molecules, which may be an ion, moves across the biological membrane, down its electrochemical gradient. This primary molecule is what allows the other molecule, possibly another ion, to move in an uphill direction, against its concentration gradient. The molecule that moves down its concentration gradient is what drives the movement of the secondary molecule across the membrane. It is because of this that the molecule that travels down its concentration gradient is known as the driving ion.

The difference between secondary active transport and primary active transport is that there is no direct utilisation of an ATP molecule in secondary transport.

There are two types of secondary active transport. One of which is where the molecules move in the same direction across the transport membrane, this is known as symport, involving symporters or exchangers[1]. The other is when the molecules are travelling in the opposite direction to each other, this type of secondary active transport is known as antiport[2].

An example of secondary active transport is the movement of glucose in the proximal convoluted tubule.

References

  1. http://biology.kenyon.edu/HHMI/Biol113/secondary_active_transport.htm
  2. http://www.physiologyweb.com/lecture_notes/membrane_transport/secondary_active_transport.html

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