What is the fluid mosaic model?

The fluid mosaic model is a description of the cell membrane. It describes a phospholipid bilayer, or double layer of phospholipids each with a hydrophilic (water attracting) head and hydrophobic (water repelling) tails.

Embedded in the membrane are proteins, cholesterol molecules, glycolipids, and glycoproteins. Binding sites on protein receptors fit signaling molecules, which relay messages into the inside of the cell. Cholesterol molecules embedded in the interior of the bilayer stabilize the membrane. Glycolipids (carbohydrates covalently bonded to lipids) and glycoproteins (carbohydrates covalently bonded to proteins) both serve as signaling molecules to tell cells apart.

The membrane is fluid because molecules are constantly moving in two directions, similar to icebergs floating in the oceans.

Small, uncharged polar molecules and small non polar molecules, such as nitrogen, pass freely across the membrane. Hydrophilic substances such as large polar molecules and ions move across the membrane through embedded channel and transport proteins. Water moves through channel proteins called aquaporins.