Cell Membrane-selectively (Semi) permeable. Controls the movement of molecules in and out of the cell. Protects the cell from its surroundings. Consists of the phospholipid bilayer and proteins
Phospholipids are a major component of cell membranes. Phospholipids form a lipid bilayer in which their hydrophillic (attracted to water) head areas spontaneously arrange to face the aqueous cytosol and the extracellular fluid, while their hydrophobic (repelled by water) tail areas face away from the cytosol and extracellular fluid. The lipid bilayer is semi-permeable, allowing only certain molecules to diffuse across the membrane.
Cholesterol is another lipid component of animal cell membranes. Cholesterol molecules are selectively dispersed between membrane phospholipids. This helps to keep cell membranes from becoming stiff by preventing phospholipids from being too closely packed together. Cholesterol is not found in the membranes of plant cells.
Glycolipids are located on cell membrane surfaces and have a carbohydrate sugar chain attached to them. They help the cell to recognize other cells of the body.
Structural proteins help to give the cell support and shape. Cell membrane receptor proteins help cells communicate with their external environment through the use of hormones, neurotransmitters, and other signaling molecules. Transport proteins, such as globular proteins, transport molecules across cell membranes through facilitated diffusion.
Glycoproteins have a carbohydrate chain attached to them. They are embedded in the cell membrane and help in cell to cell communications and molecule transport across the membrane.