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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

↓

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

↓

ATP phosphorylates the pump, and ADP leaves

↓

Conformational change

↓

Closes pathway from inside

↓

Pathway opens to outside

↓

Na dissociates into extracellular fluid

↓

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

↓

Acylphosphate is hydrolyzed and phosphate is released

↓

Causes closure of the pump from outside

↓

New ATP binds

↓

Opens the pump to inside

↓

2 K ions are released into the cell

↓

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

↓

Intracellular concentration of Na decreases

↓

Concentration gradient is developed for Na from outside to inside

Potassium:

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

↓

Intracellular K concentration increases

↓

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

↓

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

↓

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

↓

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

↓

Entry of Na and K

↓

Increased osmolarity inside the cell

↓

Entry of water

↓

Cell swells

↓

Cell bursts

How Na-K ATPase Prevents This?

Na-K ATPase pump

↓

Moves 3 Na out and 2 K in during each cycle

↓

Net exit of one ion during each cycle

↓

Continuous activity causes net exit of ions

↓

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

↓

Osmolarity is maintained

↓

No entry of extra water

↓

Cell volume is maintained

↓

Thats it. What else do you want?😝

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▶️ Diffusion vs Active Transport