Practice Questions

TLS Online TPP Program

#Question id: 2255

Following statements are regarding to the Na+/K+ ATPase maintains the intracellular Na+ and K+ concentrations in animal cells. Which of the following statement is incorrect?

#Unit 2. Cellular Organization

In its E1 conformation, the Na+/K+ ATPase has three high-affinity Na+-binding sites and two low-affinity K+-binding sites accessible from the cytosolic surface of the protein. The Km for binding of Na+ to these cytosolic sites is 0.6 mM, a value considerably lower than the intracellular Na+ concentration of ~12 mM; as a result, Na+ ions normally fully occupy these sites.
the affinity of the cytosolic K+-binding sites is low enough that K+ ions, transported inward through the protein, dissociate from E1 and enter the cytosol despite the high intracellular K+ concentration.
During the E1 → E2 transition, the three bound Na+ ions gain access to the exoplasmic face, and simultaneously, the affinity of the three Na+-binding sites drops. The three Na+ ions, now bound to low-affinity Na+ sites, dissociate one at a time and enter the extracellular medium despite the high extracellular Na+ concentration.
Transition to the E2 conformation generates two low-affinity K+ sites accessible from the exoplasmic face. Because the Km for K+ binding to these sites (0.2 mM) is lower than the extracellular K+ concentration (4 mM), these sites will fill with K+ ions as the Na+ ions dissociate.