• Make up cell membranes • Only 2 fatty acids attached to a glycerol • Third –OH group of glycerol is joined to a phosphate group – Negative charge • More small molecules can join to phosphate to make different phospholipids – Often polar or charged

• Two ends of phospholipids behave differently in water – Hydrocarbon tails are hydrophobic – Phosphate group and its attachments form hydrophilic head • Self-assemble into a bi-layer in water – Hydrophobic portions shielded from water

• At surface of cell, phospholipids arranged in bilayer – Heads in contact with aqueous solutions inside and outside of cell