Question

Consider the transport of Naº and K across the cell membrane by the NaK ATPase. A cell membrane generally is polarized with the inside negative. The following are all components used t calculate AG. Which of these components contributes to a more spontaneous AG? O RT In([Naou] /[Na inj) ORT IN([K]2/[koud) Z Na FAY ZiK FAY

Answer 1

free energy change in movements ions across cell membrane has two components :

1. Concentration Change (Concentration Gradient)

2. charge differences across the membrane (membrane potential)

The (Na⁺ – K⁺ )–ATPase pump,  pumps 3 Na⁺ out of and 2 K⁺ into the cell in with hydrolysis of ATP. T overall 3 Na⁺ (in) + 2 K⁺ (out) + ATP + H₂O →3 Na⁺ (out) + 2 K⁺ (in) + ADP + Pi

Answer for this question is last one : z_(k⁺⁾ F $\Delta \Psi$

(a) RT ln ((Na⁺ (out))³ / (Na⁺ (in))³ ) ; conc. of sodium ion is 9-folds outside so it gives rise to large +ve value of free energy.

(b) RT ln ((K⁺ (in))² / (K⁺ (out))² ) ; conc. of Kion is 20-folds inside so it also gives rise to large +ve value of free energy.

(c) z_(Na⁺⁾ F $\Delta \Psi$ , since cell is polarized with negative inside, here movement of ions is inside to outside ;  $\Delta \Psi$ = (out)-(in) = +ve,  it also gives rise to +ve value of free energy.

(d)z_(k⁺⁾ F $\Delta \Psi$ , since cell is polarized with negative inside, here movement of ions is outside from inside ; $\Delta \Psi$ = (in)-(out) = -ve, thus it will give rise to -ve value of free energy ; thus thiis component contributes to more spontaneous  $\Delta$G.