ATP hydrolysis in many living cells has a ΔG of -12 kcal/mol. The Na+
/glucose
cotransporter uses the energy of the plasma membrane sodium gradient to drive transport
of glucose into the cell, even if the concentration of glucose inside the cell is already higher
than outside. Hypothetically, how many Na+
ions would have to cross the membrane in each
transport cycle to provide a free energy change comparable to that of ATP hydrolysis? Use
the following conditions: external Na+
= 125 mM; internal Na+
= 12.5 mM; T= 37o
C;
membrane potential = -68 mV.

Question

ATP	hydrolysis	in	many	living	cells	has	a	ΔG	of	-12	kcal/mol.	The	Na+
/glucose	
cotransporter	uses	the	energy	of	the	plasma	membrane	sodium	gradient	to	drive	transport	
of	glucose	into	the	cell,	even	if	the	concentration	of	glucose	inside	the	cell	is	already	higher	
than	outside.	Hypothetically,	how	many	Na+
ions	would	have	to	cross	the	membrane	in	each	
transport	cycle	to	provide	a	free	energy	change	comparable	to	that	of	ATP	hydrolysis?	Use	
the	following	conditions:	external	Na+
=	125	mM;	internal	Na+
=	12.5	mM;	T=	37o
C;	
membrane	potential	=	-68 mV.