The cell membrane is a selectively permeable structure that surrounds the cell, maintaining its integrity while regulating the movement of substances. The most widely accepted model of the cell membrane is the fluid mosaic model, proposed by Singer and Nicolson in 1972.
Structural Model of the Cell Membrane (Fluid Mosaic Model)
The cell membrane is composed of a phospholipid bilayer, where the hydrophilic heads face outward and the hydrophobic tails face inward, preventing the free passage of water-soluble molecules.
Proteins are embedded in the membrane, playing roles in transport, communication, and enzymatic reactions.
Cholesterol molecules are interspersed within the bilayer, adding stability and flexibility to the membrane.
Carbohydrates are attached to proteins (glycoproteins) and lipids (glycolipids), functioning in cell recognition and signaling.
Roles of the Cell Membrane
1. Selective Permeability – The membrane regulates what enters and exits the cell, maintaining an internal balance of nutrients and ions.
2. Communication – Embedded receptor proteins receive chemical signals from other cells, triggering cellular responses.
3. Transport Mechanism – The membrane uses passive transport (diffusion, osmosis, facilitated diffusion) and active transport (endocytosis, exocytosis, pumps) to move substances.
4. Cell Recognition – Glycoproteins and glycolipids help the immune system distinguish between self and foreign cells.
5. Structural Support – The membrane provides shape and anchors the cytoskeleton.