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, mucin, and intrinsic factor. The pH of gastric juice is acidic, between 1-3. If the pH of gastric juice is 2.4. what is the amount of energy (AG) 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 -60.0 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- V^-1- mol^-1 and the gas constant is 8.314times 10^-3 kJ middot mol^-1 K^-1. Express your answer in kJ/mol.

Explanation / Answer

pH = 2.4

dG for ions pH = 7.3

Epotential = -60*10^-3 V

we must use:

dG = RT*ln(C1/C1) * Z*F*dY

so..

pH = 2.4 to 7.4

[H+]in = 10^-2.4

[H+]out = 10^-7.4

Keq = [H+]out / [H+]in

Keq = (10^-7.4)/(10^-2.4) =0.00001

so

dG1 = -RT*ln(Keq)

dG = -(8.314)(37+273)*ln(0.00001 = 29672.72 J/mol = 29.67 kJ/mol

For...

E° = 60*10^-3

dG2 = --> -nFE° = -1*96.5*(-60*10^-3) = 5.79 kJ

so..

dG = DG1 + DG2 = 5.79 +29.67

dG = 35.46 kJ/mol

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