Active transport involves the movement of materials against a concentration gradient and requires an expenditure of energy

This energy may be harnessed by one of two means:

  • The direct hydrolysis of ATP (primary active transport)
  • By coupling with the transport of another molecule moving along its electrochemical gradient (secondary active transport)

The coupled transport of two distinct molecules is called co-transport (the movement of a single molecule is called uniport)

  • If the two molecules are transported in the same direction it is called symport
  • If the two molecules are transported in opposite directions it is called antiport

The sodium-potassium pump is an example of an antiporter as sodium and potassium are pumped in opposite directions

  • This is primary active transport as both molecules are pumped against their gradient and require ATP hydrolysis

Glucose uptake in the kidneys is an example of symport as its movement is coupled to the parallel transport of sodium

  • This is secondary active transport as the sodium is moving passively down an electrochemical gradient  

Types of Cotransport