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๐Ÿ“š > Physiology > General Physiology > Transport of Substances Through Cell Membrane_>

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

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

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ATP phosphorylates the pump, and ADP leaves

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Conformational change

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Closes pathway from inside

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Pathway opens to outside

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Na dissociates into extracellular fluid

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

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Acylphosphate is hydrolyzed and phosphate is released

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Causes closure of the pump from outside

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New ATP binds

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Opens the pump to inside

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2 K ions are released into the cell

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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

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Intracellular concentration of Na decreases

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Concentration gradient is developed for Na from outside to inside


Potassium:

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

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Intracellular K concentration increases

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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

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

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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

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

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Entry of Na and K

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Increased osmolarity inside the cell

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Entry of water

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Cell swells

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Cell bursts


How Na-K ATPase Prevents This?

Na-K ATPase pump

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Moves 3 Na out and 2 K in during each cycle

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Net exit of one ion during each cycle

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Continuous activity causes net exit of ions

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

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Osmolarity is maintained

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No entry of extra water

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Cell volume is maintained

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Thats it. What else do you want?๐Ÿ˜

ย 

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โ–ถ๏ธ Diffusion vs Active Transport
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