Cell Membrane Lipid Bilayer

The cell membrane lipid bilayer, also known as the phospholipid bilayer, is a fundamental structural component of all biological membranes. It forms a continuous double layer that separates the interior of the cell from its external environment and also defines internal compartments within eukaryotic cells. The bilayer consists primarily of two layers of amphipathic phospholipid molecules. Each molecule has a hydrophilic (water-attracting) phosphate head and two hydrophobic (water-repelling) fatty acid tails. The hydrophilic heads face outward toward aqueous environments both inside and outside the cell, while the hydrophobic tails point inward, away from water, creating a stable barrier. In addition to phospholipids, other lipids such as cholesterol and glycolipids are present. Membrane proteins are embedded within or associated with this lipid matrix. It acts as a selective barrier: Prevents free passage of most water-soluble (hydrophilic) molecules while allowing certain small nonpolar molecules (e.g., O₂ and CO₂) to diffuse freely across it. Maintains distinct internal environments by controlling ion concentrations and pH through specialized transport proteins such as ion pumps and channels. Lipid molecules can move laterally within each layer ("fluid mosaic model"), allowing dynamic changes in membrane shape and protein distribution. Certain lipids serve as docking sites for proteins or act as precursors for signaling molecules when cleaved by enzymes activated by extracellular signals. Lipid rafts: Microdomains enriched in cholesterol/sphingolipids that organize specific proteins involved in signal transduction or trafficking functions. These regions contribute to functional compartmentalization within the plasma membrane itself.

Other names

Phospholipid BilayerLipid Bilayer