Cell Transport

Master answer

Transmembrane Transport Mechanisms

[table id=E-01 /]

Na⁺/K⁺ – ATPase pump

• Found in virtually all cells of the body – It is a heterodimer integral membrane protein that spans the entire membrane:
  • α-subunit (larger subunit) – Binds Na⁺, ATP and PO₄^3- intracellularly, and K⁺ and ouabain/glycosides extracellularly
  • β-subunit (smaller subunit) – A glycoprotein
• Functions as an “electrogenic pump” as it extrudes 3 Na⁺ from the cell and takes in 2 K⁺ per ATP hydrolysed
• Process of pump function:
  • Na⁺ and ATP bind to α-subunit intracellularly
  • ATP is hydrolysed to ADP and the phosphate is transferred to an Asp-phosphorylation site
  • Conformational change of the protein causes Na⁺ to be extruded into ECF
  • K⁺ binds to the α-subunit extracellularly
  • Dephosphorylation of the Asp-phosphorylation site causes the protein to return to its resting conformation, which then transports K⁺ intracellularly
• Pump function is inhibited by ouabain and digitalis glycosides

JC / Mooney / Bianca 2019

Answer by Bianca, JC, Mooney