How does Primary and Secondary Active Transport work?How are they related and how are they different?

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selmasharafaz eNotes educator| Certified Educator

Active transport is the movement of any type of molecule across a cell membrane against its concentration gradient. This is used for accumulation of molecules like ions, glucose, amino acids etc. in cells. The process is energy dependent.

The two types of active transport are :

  • Primary active transport - It uses chemical energy such as ATP, redox energy or photon energy as the driving force.
    eg. Sodium-Potassium pump that maintains cell potential.
          Mitochondrial Electron Transport Chain.
  • Secondary active transport - It uses energy generated by an electrochemical gradient (a potential difference created by pumping ions out of the cell) as the driving force. The pumping out of ions from high concentration to low concentration increases entropy.
    eg. Sodium-Glucose cotransport for intestinal absorption of glucose.

In primary active transport, transmembrane protein pumps (usually ATPases) are involved in carrying the molecules across the membrane. But in secondary active transport, pore forming proteins that form channels through the membrane are involved in transport.

Secondary active transport is also called cotransport or coupled transport. Antiport (transporting one molecule into the cell while another molecule is cotransported out of the cell) and Symport (transporting two molecules to one side of the cell together) are associated with it.

Thus Primary and Secondary Active Transport are related in the fact that both are active transport that requires energy as the driving force.
They are also related in the matter that the Primary Active Transport itself can generate the electrochemical gradient that could drive the Secondary Active Transport.