Practice question

Proposed by S.J. Singer and G.L. Nicolson in 1972 based on freeze-fracture electron microscopy and cell fusion experiments, the Fluid Mosaic Model describes membrane as two-dimensional solution where amphipathic lipids form viscous fluid matrix, about 100-fold more viscous than water, within which integral membrane proteins float as mosaic of diverse functions including pumps, receptors, adhesion molecules, and enzymes. Phospholipids exhibit rapid lateral diffusion around 10^-8 cm2 per second, rotation around axis, flexing of chains, but slow transverse flip-flop unless catalyzed by flippases, evidence obtained by Frye-Edidin heterokaryon fluorescence showing intermixing of human and mouse antigens within minutes and later fluorescence recovery after photobleaching revealing mobile fraction. Peripheral proteins attach via electrostatic interactions with anionic headgroups or protein-protein interactions via adapters. Lipid composition variation creates phase coexistence: saturated sphingolipids and cholesterol form ordered microdomains rafts. Mosaic arrangement allows remodeling during endocytosis, formation of immunological synapse, and diffusion-reaction signaling. Membranes are not static crystalline arrays of Davson-Danielli sandwich nor composed solely of phospholipids, but dynamic mosaics enabling compartmentalization and adaptability essential for life.