Question

The plasma membrane of a cell has a surface charge density of 2 x 10-4 C/m2 on the outside and an equal magnitude, opposite sign charge density on the inside. The membrane is approximately 5 nm thick. (a) Is the potential difference from the inside of the cell to the outside positive or negative? Explain briefly. (b) How much energy is required for a sodium-potassium pump (the enzyme that transfers Na+ ions from the inside of the cell to the outside, and K+ from the outside to the inside) to transport three Na+ ions from the inside to the outside of the cell? (Assume the energy required is just equal to the electric potential energy gained by the Na+ ions in moving from the inside to the outside; ignore the energy associated with conformational changes to the enzyme.) The charge of each ion is the elementary charge.

          The plasma membrane of a cell has a surface charge density of 2
x 10-4 C/m2 on the outside and an equal magnitude, opposite sign
charge density on the inside. The membrane is approximately 5 nm
thick. (a) Is the potential difference from the inside of the cell
to the outside positive or negative? Explain briefly. (b) How much
energy is required for a sodium-potassium pump (the enzyme that
transfers Na+ ions from the inside of the cell to the outside, and
K+ from the outside to the inside) to transport three Na+ ions from
the inside to the outside of the cell? (Assume the energy required
is just equal to the electric potential energy gained by the Na+
ions in moving from the inside to the outside; ignore the energy
associated with conformational changes to the enzyme.) The charge
of each ion is the elementary charge.

Added by Lauren T.

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