Gastric juice is made up of substances secreted from parietal cells, chief cells

Question

Gastric juice is made up of substances secreted from parietal cells, chief cells, and mucous-secreting cells. The cells secrete HCI, proteolytic enzyme zymogens, much, and intrinsic factor. The pH of gastric juice is acidic, between 1-3. If the pH of gastric juice is 1.2, what is the amount of energy (Delta G) required for the transport of hydrogen ions from a cell (internal pH of 7.4) into the stomach lumen? Assume that the potential difference across the membrane separating the cell and the interior of the stomach is -70.0 mV (inside of cells negative relative to the lumen of the stomach) Assume that the temperature is 37 degree C. The Faraday constant is 96.5 kJ middot V^-1 and the gas constant is 8.314 times 10^-3 middot K^-1. Express your answer in kJ/mol.

Explanation / Answer

Get H+ from each:

[H+]in = 10^-pH1 = 10^-1.2 = 0.063095 M

[H+]out = 10^-pH2 = 10^-7.4 = 3.98*10^-8 M

how

K = [H+]2/[H+]1

K = (3.98*10^-8)/(0.063095 ) = 6.3079*10^-7

we know

dG1 = -RT*ln(Keq)

T = 273+37 = 310 K

dG1 = -RT*lnK

dG1 = -8.314*310*ln(6.3079*10^-7)

dG1 = 36794.860 J = 36.79 kJ

For faraday constant:

F = 96.5 kJ /(V-mol)

so

E = -70*10^-3 V (given) n = 1 electron,

dG2 = -nFE° = -1*96.5*(-70*10^-3) = 6.75 kJ

now

total dG

dG = dG1+dG2 = 36.79 +6.75 = 43.54 kJ/mol

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