The Plasma Membrane
All living cells are surrounded by a cell surface membrane, or plasma membrane, in addition to the possibility of a cell wall and, in bacteria, a capsule. It has the function of controlling substances entering and exiting the cell as well as keeping the cell’s organelles and other parts within. Many other membranes within eukaryotic cells are also very similar to the plasma membrane. Membranes are composed of phospholipids, proteins and carbohydrates in a fluid mosaic structure.
The phospholipids form a bilayer which is flexible. Within this float the proteins and carbohydrates may extend from these.
The phospholipid bilayer is formed of two layers of phospholipids with a polar hydrophilic phosphate head on the exterior and a fatty acid hydrophobic tail in the middle of the membrane. The hydrophobic tails act as a barrier to water between the two layers, effectively isolating them from each other. Other membranes contain phospholipids too, but the fatty acid chains are variable which changes the…