Lipid bilayer

The Lipid bilayer is a universal component of all cell membranes. Its role is critical because its structural components provide the barrier that marks the boundaries of a cell. The structure of the lipid bilayer explains its function as a barrier. Lipids are fats, like oil, that are insoluble in water. There are many types of lipids, but they all possess a hydrophilic ('water loving') head and one or two hydrophobic ('water fearing') tails. These properties allow lipid bilayers to self-assemble into a double layer (bilayer) in water, with the hydrophobic tails pointing inward and the hydrophilic heads pointing outward.

Structure

The lipid bilayer is composed primarily of phospholipids, which consist of a hydrophilic head and a hydrophobic tail. The hydrophilic head is attracted to water, while the hydrophobic tail repels water. When placed in water, phospholipids form a bilayer, with the hydrophilic heads facing the water and the hydrophobic tails facing each other. This forms a barrier that prevents the free passage of most molecules into and out of the cell.

Function

The primary function of the lipid bilayer is to provide a barrier between the cell and its environment. This barrier is selectively permeable, allowing some substances to pass through while keeping others out. This selective permeability is vital for the proper functioning of the cell, as it allows necessary substances like nutrients and oxygen to enter the cell, while keeping harmful substances out.

Properties

The properties of the lipid bilayer are determined by the nature of the phospholipids that make up the bilayer. The length and saturation of the fatty acid chains can affect the fluidity of the membrane, with longer and more saturated chains making the membrane more rigid. The presence of cholesterol can also affect membrane fluidity, as well as its permeability to small, water-soluble molecules.

See also

• Cell membrane
• Phospholipid
• Membrane fluidity

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