top of page

Primary vs Secondary Active Transport



  • In primary active transport, the energy comes directly from the ultimate source.

  • In secondary active transport, the energy comes from the ultimate source only, but indirectly.


Analogy of Mountain


We take a rock from base to the top of mountain

↓ The energy that we put in to take rock uphill, is stored in the rock in form of its high altitude

↓

Tie this rock to another rock at the base with a rope

↓

Let the top rock roll down the hill

↓

The rope pulls the second rock from bottom to top

  • Here the ultimate source of energy is us.

  • Movement of first rock is primary active because we are putting our energy directly on it.

  • The energy that we have put is stored in the rock as potential energy.

  • Movement of second rock is secondary active because the energy that we have put in the first rock is secondarily used to move that rock.

  • If we tie the second rock to a third rock and let the second rock roll down to move third rock up, the movement of third rock would be called tertiary active transport.


Example of Na-Ca Exchanger


Na-K ATPase pump moves Na from inside to outside of the cell using energy from ATP

↓

Energy from ATP is stored in Na outside the cell, in form of its high concentration

↓

Na-Ca exchanger is like a rope that couples Na and Ca movement

↓

It lets the Na diffuse down the concentration gradient

↓

Uses the energy from this downhill movement to push Ca uphill

  • Here the ultimate source of energy is ATP.

  • Movement of Na by Na-K ATPase pump is primary active because it uses ATP directly.

  • The energy that ATP has put, is stored in form of an electrochemical gradient of Na.

  • Movemnet of Ca by Na-Ca exchanger is secondary active because the energy that ATP has put on Na is secondary is used to transport Ca.

  • This stores the energy in Ca. Now if we use this energy from Ca to move a third substance uphill, it would be called tertiary active transport.

 

Next >>

Comments


bottom of page