PS1-08answ

# PS1-08answ - Name Section TA Problem Set 1 Biochemistry...

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Name: ________________________ TA: __________________________ Section: _______________________ Problem Set 1 Biochemistry 462b Spring 2008 Due Jan 25, 2007 Question 1. (3 points) The parietal cells of the stomach lining contain membrane pumps that transport hydrogen ions from the cytosol of these cells (pH 7.0) into the stomach, contributing to the acidity of gastric juice (pH 1.0). Calculate the free energy required to transport 1 mol of hydrogen ions through these pumps. Assume a temperature of 37 °C and a neutral electrochemical gradient across the membrane. Ans : The reaction is written as C inside C outside Since there is no chemical transformation involved in the transport of H + across a membrane, at equilibrium the Δ G'° is zero (- RT ln(1/1) = 0). The intracellular H + concentration is 10 -7 M and outside of the cell is 10 -1 M. Δ G = Δ G'° + RT ln (10 -1 M/10 -7 M) = 0 kJ/mol + (2.58 kJ/mol) ln (10 -1 M/10 -7 M) = 35 kJ/mol Question 2. (4 points) Cells typically have low [Na + ] (12 mM) inside and much higher [Na + ] outside (145 mM). The Na + K + ATPase maintains the Na + gradient, causing the inside to be negative (-70 mV) relative to the outside of the cell. The free energy driving the entry of Na + into the cell results from both the concentration gradient ( Δ Gc) and membrane potential ( Δ Gm). Calculate the contribution to Δ G from each, and well as the total free energy difference across the membrane resulting from the Na+ ion gradient. Assume the system is at 20°C. Ans

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## This homework help was uploaded on 04/02/2008 for the course BIOC 462b taught by Professor Grimes,tsao,borque during the Spring '08 term at Arizona.

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PS1-08answ - Name Section TA Problem Set 1 Biochemistry...

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