The sodium potassium pump transports 2 potassium ions (K+) inside the cell and 3 sodium ions (Na+) outside the cell by the hydrolysis of ATP into ADP. The break down of ATP occurs because it generates an inorganic phosphate. This inorganic phosphate is crucial for the phosphorylation of the Na+/K+ pump to activate it.
The sodium potassium pump cannot be classed as co-transporter because the Na+/K+ pump transports both the ions against the concentration gradient whereas, a cotransporter transports one substance down the concentration gradient and the other against.
An regulated proton transport would never develop a proton gradient. This would hamper processes like the synthesis of ATP and sucrose co-transport that require a H+ gradient.
Explanation:
Working of Sodium/Potassium Pump (NA+/K+) Pump:
The sodium potassium pump is a transmembrane transport channel that actively transports Na+ and K+ ions in and out of the cell to develop a concentration gradient.
The NA+/K+ pump contains the enzyme Na+/K+ ATPase that hydrolyses (breaks down in presence of water) ATP into ADP and inorganic phosphate (Pi).
The inorganic phosphate phosphorylates the transport proteins causing a change in conformation.
This energy (in the form of inorganic phosphate) is used to actively transport 2 potassium ions inside the cell and 3 sodium ions outside. This maintains a concentration gradient of the two ions at rest. This unbalanced charge maintains the resting membrane potential on the membrane of the neuron.
A reversal of the membrane potential i.e. more K+ outside and more Na+ inside the cell generates an action potential on the membrane.
This action potential is the nerve impulse that travels throughout the nervous system.
Co-transporter:
A co-transporter is a sub-class of transport channels that transports two substances at the same time, one down its concentration gradient and the other against.
Symporters and uniporters are types of co-transporters.
A Na+/K+ pump cannot be classed as a co-transporter as it transports both sodium and potassium ions against their concentration gradient by the break down of ATP.
Proton (H+) Gradient:
A proton gradient is essential for the production of ATP by the process of cellular respiration.
The enzyme responsible for ATP generation, ATP synthase is a molecular motor that couples the proton gradient generated by proton transporters and the energy produced by the break down of ATP into ADP to produce more ATP.
