流動モザイクモデル

The fluid mosaic model describes the plasma membrane as a flexible structure made up of lipids, proteins, and carbohydrates.

It is called “fluid” because some molecules, such as phospholipids and some proteins, can move sideways within the membrane, and “mosaic” because a mix of proteins, lipids, and carbohydrates is scattered throughout, giving the membrane a patchwork-like appearance.

Together, these components contribute to the cell’s structural integrity and allow functions that require membrane flexibility.

First, let's discuss the most abundant component, lipids, which include both phospholipids and cholesterol.

Phospholipids consist of a hydrophilic, water-loving head and two hydrophobic, water-fearing fatty acid tails.

These molecules spontaneously form a lipid bilayer, with hydrophobic tails facing inward and hydrophilic heads facing outward. This arrangement separates the inside of the cell from the outside environment.

Cholesterol molecules are found between the phospholipids and help maintain membrane fluidity and stability.

The second major component is proteins, which can associate with the lipid bilayer to help move substances and pass signals across the membrane.

Integral proteins are embedded within the membrane, and many span the entire bilayer. Peripheral proteins, on the other hand, often attach temporarily to the inner or outer surface of the membrane.

The final component, carbohydrates, are found on the outer surface of the membrane.

They can bind to proteins to form glycoproteins or to phospholipids to form glycolipids.

Together, these carbohydrate complexes form the glycocalyx, a sugar coating that plays a key role in cell recognition and communication.