Gastric juice (pH 1.5) is produced by pumping HCl from blood plasma (pH 7.4) int

Question

Gastric juice (pH 1.5) is produced by pumping HCl from blood plasma (pH 7.4) into the stomach

Part A
Calculate the amount of free energy required to concentrate the H+ in gastric juice at 37 ºC based on the concentrations calculated from the above pH values. Express your answer as an integer in cal/mol.

Part B
Under cellular conditions, how many moles (whole #) of ATP must be hydrolyzed to provide this amount of free energy (from Part A)? Assume the free-energy change (G) for ATP hydrolysis under cellular conditions is about -13 kcal/mol. Ignore the effects of the transmembrane electrical potential.

Explanation / Answer

Explanation:

Part A - Solution

The pH of Gastric Juice is given as = 1.5

As we know that pH = -log [H+] => [H+] = 10 –pH H+ concentration in Gastric juice is = 10-1.5 = 0.0316 M The pH of blood plasma is given as = 7.4 H+ concentration in blood plasma is = 10-7.4 = 3.98 * 10-8 M For calculating free energy change, Gt, to transport HCl from blood plasma to gastric juice we need to use the below formula, G = Go + RT ln{["product"]/["reactant"]} ["product"] - Solute concentration in final product ["reactant"] - Solute concentration in source R - gas constant = 8.314 J/mol.K = 1.987 cal / mol*K T - Temperature, K = 273 + 37 C = 310 K (given temperature as 37 C) In transport process, Go = 0, as solute is same in both reactant and product So, the above equation comes to G = RT ln{["product"]/["reactant"]} In our given problem, the product is gastric juice and the reactant is blood plasma. So the equation comes down to, Gt = RT ln{[H+]gastric juice / [H+]blood} => Gt = RT ln{0.0316 M / 3.98*10-8 M } = (1.987 cal/mol.K) * (310 K) * 13.585 = 8368 cal/mol Therefore, the free energy required to concentrate H+ in gastric juice is 8368 cal/mol.

Part B:Solution

From the above problem, we require 8.368 Kcal/mol of free energy to get gastric juice. Given that the free-energy change (G) for ATP hydrolysis under cellular conditions is = -13 kcal/mol So by hydrolyzing 1 ATP molecule we get -13 Kcal/mol For the above cellular conditions and reaction, the free energy required is 8.368 Kcal/mol No. of moles of ATP required = 8.368/13 = 0.64 moles. When taken as whole no. it comes as 1. Therefore the number of moles of ATP required to get free energy required for above action = 1

Related Questions

Navigate

• Browse (All)
• Browse G
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.