Question

What is the free energy change in transporting an uncharged molecule across the membrane of a cell from 10^-5 M to 10^-2M? Is an input of free energy required for this transport?

Answer 1

The equation for free energy change of transport across the membrane for the uncharged molecule is:

Where R= gas constant=1.987 cal/mol K; T= standard tempearature= 298 K; [S]_sideB= concentration of substrate on one side of the membrane (say B side), [S]_sideA=concentration of the substrate on the other side of the membrane, from where the substrate is coming (say A side)

We will use the values of R and T as stated above, and the given values of the solute : [S]_sideB=10^-2 M (recipient), [S]_sideA= 10^-5 M (sender).

By putting these values we get,

or,

or,

or,

or,

or,

=4090.288 calorie/mol.

4.1 kcal/mol.

Since the value of this transport process is positive. the reaction is not spontaneous. Hence, energy input is required for this transport i.e. movement of solute having 10^-5 M concentration to the side where its concentration is 10^-2 M.