CELL MEMBRANE

• The membrane surrounding a cell, called the plasma membrane, forms the boundary that separates the living cell from its non-living surroundings.
• The plasma membrane, which is only about 8 nm thick, selectively controls the movement of materials into and out of the cell.
• The plasma membrane is responsible for cell-cell recognition, for example when cells aggregate into tissues.
• The currently accepted model for the structure of the plasma membrane and cellular membranes generally is the fluid mosaic model.
• In the fluid mosaic model, there is a double layer of phospholipids, which are arranged with their hydrophobic tails facing inwards.
• The double layer of lipids in the fluid mosaic model is quite fluid, with proteins floating within it.
• Glycolipids, glycoproteins, and cholesterol are also an integral part of the membrane structure.
• Some proteins, called peripheral proteins, are stuck to the surface of the membrane.
• Glycolipids act as surface receptors and stabilize the membrane.
• Some proteins completely penetrate the phospholipid layer and may control the movement of specific molecules into and out of the cell.
• Glycoproteins play an important role in cellular recognition and immune responses and help stabilize the membrane structure.
• Cholesterol in the membrane disturbs the close packing of the phospholipids and keeps the membrane more fluid.
• Some substances, particularly ions and carbohydrates, are transported across the membrane via the proteins.
• Some substances, including water, are transported directly through the phospholipid bilayer.
• Glycolipids also have a role in helping cells to aggregate in the formation of tissues.
• Membranes fulfill a role in recognition and communication between cells, allowing ‘like’ cells to form tissues and organs.
• Membranes allow the body to distinguish foreign material from its own tissue.
• Some membranes are involved in membrane transport, where materials required by the cell are imported into the cell and waste products are removed from the cell.
• The plasma membrane surrounds the cell and has an important role in containment, transport, signaling and communication.
• Membranes are also found within eukaryotic cells as part of the structure of membranous organelles such as mitochondria, nucleus, Golgi apparatus, endoplasmic reticulum, vesicles, and vacuoles.