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Na-K-ATPase Pump



  • Sodium concentration is higher outside the cell.

  • Potassium concentration is higher inside the cell.

Na-K ATPase pump:

  • Moves sodium from inside to outside the cell against electrochemical gradient.

  • Moves potassium from outside to inside of the cell against electrochemical gradient.

  • Uses ATP for this active transport.

  • Such transport using ATP is an example of primary active transport.


Structure

  • 3 sites for sodium (Na)

  • 2 sites for potassium (K)


Catalytic Cycle

During each cycle:
  • 3 Na ions move from inside to outside.

  • 2 K ions move from outside to inside.

  • 1 ATP is hydrolyzed into ADP and phosphate.

Steps

Starting from a state when an ATP is bound to the pump, the permeation pathway is open to the inside, and all the sites are empty

โ†“

3 Na ions from the cell bind to the Na-binding sites

โ†“

ATP phosphorylates the pump, and ADP leaves

โ†“

Conformational change

โ†“

Closes pathway from inside

โ†“

Pathway opens to outside

โ†“

Na dissociates into extracellular fluid

โ†“

2 K ions from extracellular fluid bind to K-binding sites

โ†“

Acylphosphate is hydrolyzed and phosphate is released

โ†“

Causes closure of the pump from outside

โ†“

New ATP binds

โ†“

Opens the pump to inside

โ†“

2 K ions are released into the cell

โ†“

The cycle is complete


Importance

Establishes Concentration Gradient for Na and K

Sodium:

Active extrusion of Na from inside to outside by Na-K ATPase pump

โ†“

Intracellular concentration of Na decreases

โ†“

Concentration gradient is developed for Na from outside to inside


Potassium:

Active uptake of K from outside to inside by Na-K ATPase pump

โ†“

Intracellular K concentration increases

โ†“

Concentration gradient is developed for K from inside to outside


Generates of Electronegativity Inside the Cell

During each cycle, Na-K ATPase pump moves 3 Na outside and 2 K inside

โ†“

Net exit of 1 positively charted ion out of the cell during each cycle

โ†“

Continuous activity of Na-K ATPase pump makes inside of the cell electronegative


Importance of Electrochemical Gradient

  • For generation and transmission of electrical impulses in excitable cells like neurons and muscle cells.

  • Electrochemical gradient of Na is used for secondary active transport of other substances e.g. sodium-glucose cotransporter uses downhill movement of Na to move glucose uphill.


Maintain Cell Volume

What Would Happen Without Na-K ATPase Pump?

Cells have proteins and some other large organic molecules that cannot move out of the cell and they carry a negative charge

โ†“

Attract positive ions like Na and K from outside to inside the cell

โ†“

Entry of Na and K

โ†“

Increased osmolarity inside the cell

โ†“

Entry of water

โ†“

Cell swells

โ†“

Cell bursts


How Na-K ATPase Prevents This?

Na-K ATPase pump

โ†“

Moves 3 Na out and 2 K in during each cycle

โ†“

Net exit of one ion during each cycle

โ†“

Continuous activity causes net exit of ions

โ†“

Balances the entry of ions that is happening due to attraction by negatively charged proteins

โ†“

Osmolarity is maintained

โ†“

No entry of extra water

โ†“

Cell volume is maintained

โ†“

Thats it. What else do you want?๐Ÿ˜

ย 

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