Phospholipids are fat derivatives in which one fatty acid has been replaced by a phosphate group and one of several nitrogen-containing molecules.
Image unavailable: Diagram of amylopectin structure with a glucose unit, linking points indicated by green and red lines. Red line shows alpha-1,6 glycosidic bonds. Molecular structure expanded at the bottom.
Example 2.4.1: Phosphatidyl ethanolamine (also known as cephalin)
The hydrocarbon chains are hydrophobic (as in all fats). However, the charges on the phosphate and amino groups (in red) make that portion of the molecule hydrophilic. The result is an amphiphilic molecule.
Image unavailable: Diagram of a lipid bilayer with blue polar heads facing outward and orange hydrocarbon tails inward. Labels indicate polar heads and tails. Surrounding areas are labeled as aqueous.
Phospholipids like phosphatidyl ethanolamine are major constituents of cell membranes. These molecules form a phospholipid bilayer with their hydrophilic (polar) heads facing their aqueous surroundings (e.g., the cytosol) and their hydrophobic tails facing each other.