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8.3.4′ The discussion of electrophoresis in Section 8.3.4 is rather na ̈ıve; the full theory is quite
involved. For an introductory discussion see Benedek & Villars, 2000c,§3.1.D; for many details see
Viovy, 2000.
8.6.1′
- Section 8.6.1 argued that a bilayer membrane will prefer to be flat. Strictly speaking, this
argument only applies to artifical, pure lipid bilayers. Real plasma membranes have significant
compositional differences between their sides, with a corresponding spontaneous tendency to bend
in one direction. - The logic given for the elastic energy of a membrane may be more familiar in the context of an
ordinary spring. Here we find the elastic (potential) energy for a small deformation to be of the
formU=^12 k(∆x)^2 ,where ∆xis the change in length from its relaxed value. Differentiating to find
the force givesf=−k(∆x), which is the Hooke relation (compare Equation 5.14 on page 152). - More realistically, bending a bilayer creates a combination of stretching the outer layer and
squeezingthe inner layer. In addition, the bilayer’s elasticity contains contributions from deforming
the tails as well as the heads of the amphiphiles. These elaborations do not change the general form
of the bending elasticity energy. For many more details about bilayer elasticity, see for example
Seifert, 1997.