The molecules that can be found in the cell membrane include:
- Phospholipids: The most abundant molecules, forming a bilayer with hydrophilic heads and hydrophobic tails. Major types are phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin. Phosphatidylinositol is also present in smaller amounts and plays a role in signaling.
- Proteins: These include integral (transmembrane) proteins that span the membrane, peripheral proteins loosely attached to the surface, and lipid-anchored proteins. They perform functions like transport, signaling, and recognition.
- Cholesterol: Interspersed among phospholipids, cholesterol regulates membrane fluidity and stability.
- Carbohydrates: Found only on the outer surface, attached to proteins (glycoproteins) or lipids (glycolipids), these molecules play roles in cell recognition and immune response.
Additionally, small molecules like water, oxygen, and carbon dioxide can permeate the membrane, while ions and larger molecules require specific transport proteins.
In summary, the cell membrane is mainly composed of phospholipids, proteins, cholesterol, and carbohydrates, which together create a dynamic and functional barrier.