It takes energy to move an uncharged solute across a porous membrane from a region of lower concentration (C1) to a region of higher concentration (C2). Equation 11.3 (below) allows one to calculate the amount of energy (in kJ per mol of solute moved), given the concentrations on each side of the membrane. [Notice that the equation includes the temperature, which for biological processes can be taken as 300K, and the gas constant (R), 8.32 J/mol*K].
To get an idea of the magnitude of energy involved in transport, calculate ΔGt (the free energy change for transport) when glucose is moved across a membrane from a region in which its concentration is 0.10 mM to a region where its concentration is 1 mM. What is ΔGt for the uptake of glucose from a region of 1 μM concentration into a cell where the concentration is 5 mM? How do these energies compare with that available from hydrolysis of a mole of ATP? What is the sign of ΔGt?
Original material from Lehninger Principles of Biochemistry, 5a edición, de D. Nelson and M. Cox; 2009. ISBN: 0-7167-7108-X.
Dr. José Antonio Encinar. (IBMC-UMH)