The fluid mosaic model represents the structure of a cellular membrane as a bilipid layer irregularly interspersed with protein in which the positions of individual bilipid and protein molecules are dynamic. In this model, lipids maintain flexibility and limit diffusion while proteins transport molecules through the membrane.
The fluid mosaic model infers the structure of cell membranes in their native state using ultrathin sectioning under electron microscopes. Newer membrane models take advantage of technology available to view single molecules, including atomic force microscopy. Stochastic optical reconstruction microscopy has broken the light diffusion barrier, capturing images of mitochondria and spindle fibers. A Protein Layer–Lipid–Protein Island model proposes a compressed outer protein layer on top of the bilipid layer and clusters of proteins inside the bilipid layer. An outer protein layer better protects the bilipid layer from environmental stresses. This layer is less flexible than the dynamic layer represented in the fluid mosaic model. Clustering on the inner side of the membrane increases protein efficiency over randomly interspersed proteins.
Membrane model accuracy improves as observational techniques advance. However, past research has focused on molecular interactions at the membrane. The models do not account for complex interactions between cells or the influence of elements within the cell.