Q. 16

[vpatel19876513]

I don't see the correlation between ATP and K+. If anything, I thought K+ would involve NADH + H+ because one of those H+ is donated to pyruvate to make lactate. Thus, if two pyruvates are the result of one glucose molecule, two H+ would be needed and ultimately, 4 K+ would need to be pumped into the cell.

[mcat_premed3832]

The line of reasoning that you presented cannot be derived from the information provided and certainly does not happen in vivo (not to mention, the events you described are not related both biochemically nor in terms of where the events occur in the cell).

Though you are responsible to know the relationship between ATP and bringing K+ into the cell (because knowing the Na-K ATPase pump is part of your responsibilities for the new MCAT), you would not even need to know that for this problem. You only need to know that anaerobic respiration would be predominant during vigorous exercise meaning 2 ATP per molecule of glucose. Then, even if you did not know about the Na-K ATPase pump, you would just look at the equation provided and use basic stoichiometry to determine that 2ATP would result in 4K+.

But, besides this question, you should have a basic understanding of this pump and its effect on helping to maintain a negative Vm by pumping a net + outside of the cell by using ATP as a source of energy. This is a classic example of active transport.

[ames.rober3649]

aren't 4 molecules of atp produced for a net of 2? so there would actually be 8 k+?

[hua8986059]

net 2 is there for a reason the 2 others are used during glycolysis so they are not applicable to this equation.