Plasma membranes are a lipid bilayer, typically with phosphate heads on each surface and long carbon tails on the inside. These carbons are neutral, and undergo hydrophobic interactions for an energetically favorable state.

Integral membrane proteins pass through this lipid bilayer, and so must be capable of interacting both with the polar solvents of intracellular and extracellular space, as well as the hydrophobic core of the layer. The transmembrane portion often has alpha-helical secondary conformation, with hydrophobic residues like glycine on the outside towards the carbon tails with polar amino acid residues tucked in.