You make a mutation in the Na+/K+ pump such that it now transports 3 K+ ions into the cell instead of two. What will be the consequence of this mutation?

Question

You make a mutation in the Na+/K+ pump such that it now transports 3 K+ ions into the cell instead of two.  What will be the consequence of this mutation?

BlackTom AI · Accepted Answer

First, consider the role of the Na+/K+ pump: it uses ATP to move ions against their gradients, typically exporting 3 Na+ ions and importing 2 K+ ions each cycle, which contributes to maintaining membrane potential and ionic gradients.
Option 1: 'ATP is no longer needed for transport' would be incorrect because the pump remains an ATP-dependent transporter; mutating the stoichiometry to move more K+ in does not remove the need for ATP hydrolysis for active transport.
Option 2: 'The pump is no longer an active transport protein' is inaccurate since the pump would still be consuming energy to move ions against their gradients, albeit with altered stoichiometry; the mechanism would still be active transport, not passive.
Option 3: 'There will be more K+ outside of the cell than inside the cell.' With the described mutation, the pump would relocate 3 K+ ions into the cell per cycle instead of 2; assuming the Na+ export aspect remains, this would actually increase intracellular K+ relative to outside, not the opposite. Therefore this statement mischaracterizes the directional outcome of the mutation.
Option 4: 'It will not generate any membrane potential' This aligns with the idea that the normal pump is electrogenic because 3 Na+ out and 2 K+ in produce a net outward positive current. If the pump now moves 3 K+ in for each cycle while possibly still exporting Na+, the net charge movement per cycle would be closer to neutral (e.g., 3 positive charges in versus 3 or 0 out, depending on exact coupling). In many plausible interpretations of the described mutation, the electrochemical current contributed by the pump would be substantially reduced or eliminated, leading to little or no direct membrane potential generation by the pump itself. Consequently, this option correctly captures the anticipated loss of the pump’s electrogenic contribution.

Thus, evaluating each choice: the first and second misstate the dependence on ATP and the activity of the pump; the third reverses the expected intracellular/extracellular distribution of potassium; the fourth accurately reflects the loss of net current generation by the altered stoichiometry, given the usual electrogenic nature of the pump. Hyperfocus on the mutation’s effect shows a shift toward neutrality of charge movement per cycle, meaning the pump would not contribute to membrane potential in the same way as the wild-type.

Bio 93 Section CDE 2025 Midterm 1- Section E

You make a mutation in the Na+/K+ pump such that it now transports 3 K+ ions into the cell instead of two. What will be the consequence of this mutation?

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