Lipids as a class of molecules display a wide diversity in structure and biological function. A primary role of lipids is to form the membrane bilayer permeability barrier of cells and organelles (Figure 1).

The properties of lipids help explain the structure of a cell because part of it is hydrophobic, the part that doesn’t allow anything in it, and part of it is hydrophilic, the part that doesn’t let anything out of the cell.

Lipids are essential for all life on Earth. They play many important roles in maintaining the health of an organism. Arguably the most important function lipids perform is as the building blocks of cellular membranes. Other functions include energy storage, insulation, cellular communication and protection.

The structure of the lipid bilayer explains its function as a barrier. Since a lipid molecule contains regions that are both polar and nonpolar, they are called amphipathic molecules. The most abundant class of lipid molecule found in cell membranes is the phospholipid.

Phospholipids spontaneously form stable bilayers, with their polar head groups exposed to water and their hydrophobic tails buried in the interior of the membrane. Lipids constitute approximately 50% of the mass of most cell membranes, although this proportion varies depending on the type of membrane.

Biological roles Membrane lipids also form a matrix in which membrane proteins reside. Historically lipids were thought to merely serve a structural role. Functional roles of lipids are in fact many: They serve as regulatory agents in cell growth and adhesion. They participate in the biosynthesis of other biomolecules.

Transportation. Membrane proteins can allow hydrophilic molecules to pass through the cell membrane. Transport membrane proteins come in many forms, and some require energy to change shape and actively move molecules and other substances across the cell membrane. They do this by releasing ATP to use as an energy source …

Biological membranes have three primary functions: (1) they keep toxic substances out of the cell; (2) they contain receptors and channels that allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the …

The components of the plasma membrane