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The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes form a continuous barrier around all cells . The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear membrane surrounding the cell nucleus , and membranes of the membrane ...
Phospholipid bilayers are the main structural component of the cell membranes. In biological membranes, the phospholipids often occur with other molecules (e.g., proteins , glycolipids , sterols ) in a bilayer such as a cell membrane . [ 7 ]
The hydrophobic core of the phospholipid bilayer is constantly in motion because of rotations around the bonds of lipid tails. [13] Hydrophobic tails of a bilayer bend and lock together. However, because of hydrogen bonding with water, the hydrophilic head groups exhibit less movement as their rotation and mobility are constrained. [13]
Non-bilayer forming lipid like monogalactosyl diglyceride (MGDG) predominates the bulk lipids in thylakoid membranes, which when hydrated alone, forms reverse hexagonal cylindrical phase. However, in combination with other lipids and carotenoids / chlorophylls of thylakoid membranes, they too conform together as lipid bilayers.
The phospholipid bilayer structure (fluid mosaic model) with specific membrane proteins accounts for the selective permeability of the membrane and passive and active transport mechanisms. In addition, membranes in prokaryotes and in the mitochondria and chloroplasts of eukaryotes facilitate the synthesis of ATP through chemiosmosis.
They are usually organized into a bilayer in membranes with the polar hydrophilic heads sticking outwards to the aqueous environment and the non-polar hydrophobic tails pointing inwards. [6] Glycerophospholipids consist of various diverse species which usually differ slightly in structure. The most basic structure is a phosphatidate.
Fluid mosaic model of a cell membrane. The fluid mosaic model explains various characteristics regarding the structure of functional cell membranes.According to this biological model, there is a lipid bilayer (two molecules thick layer consisting primarily of amphipathic phospholipids) in which protein molecules are embedded.
Hence, the layer is called a phospholipid bilayer, or sometimes a fluid mosaic membrane. Embedded within this membrane is a macromolecular structure called the porosome the universal secretory portal in cells and a variety of protein molecules that act as channels and pumps that move different molecules into and out of the cell. [2]