Figure 4.

Molecular geometry of lipids and membrane stored stress. Monolayers made of cylindrical molecules of zero spontaneous curvature (SC) can form nonstressed lamellas (first column, green lipid). However, for nonzero SC, lipid molecules have to be reshaped to fit into a flat state, leading to membrane stress (second column, orange lipid). When the stress accumulated in the resulting bilayer is too big, the transition of the lamella into a nonlamellar phase is favorable. The transition begins when small interlamellar contacts having characteristic hourglass shape form (third column, red lipid), lipids with negative SC promotes formation of these localized nonbilayer structures [12].