Consider a phospholipid bilayer membrane consisting of a mixture of 90% uncharge

Question

Consider a phospholipid bilayer membrane consisting of a mixture of 90% uncharged lipid and 10% of singly-negatively charged acid lipids. Assume 0.7 nm2 surface area per lipid head group, and assume further that the charged lipids are uniformly distributed and immobile. The membrane is in contact with an aqueous solution of NaCl at 25 C. The salt concentration is 110 mM . For this problem we will use a simple model for the field screening charge.

Calculate the areal charge density (i.e. charge per unit surface area) of the membrane.

Assume that the region of charge imbalance is 1 nm in thickness and that the charge distribution is uniform in that region, calculate the concentration of positive charge in the 1 nm-region close to the cell membrane.

Explanation / Answer

One in 10 lipid has a charge of -e.

Charge per unit surface area = -e/10 x surface area

= -e/10 x 0.7 nm2

= -e/7

= - 0.14 e/nm2.

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