Plasma membrane
A plasma membrane encapsules each and every cell. The plasma membrane is necessary to allow different concentrations of substances to be maintained between the cell and it's environment. Eukaryotic cells have internal membranes which surround organelles, allowing different constituent concentrations within the cell.
The structure of the plasma membrane is made up of a lipid bilayer embedded with proteins and cholesterol. Most lipid bilayers are comprised of phospholipids, the most common being phosphatidylcholine. The head part of it is made up of a phosphate and a hydrophilic choline, the tail component of the phospholipid is comprised of two fatty acid chains, long hydrocarbon structures with a chemically active COOH. Since the head is hydrophilic and the tails are hydrophobic, the phospholipid is said to be amphipathic. The structure of the bilayer is such that the tails are shielded from contact with water, creating a selectively-permeable barrier.
The plasma membrane has many functions and is a fundamental part to the cell. It communicates with the environment and other cells by means of a glycocalyx, a system of protein-linked and lipid-linked carbohydrates. It allows passage of selective molecules in and out of the cell via carrier or channel proteins embedded within the membrane, and it regulates cell growth, shape change, movement and division.
The membrane is associated with proteins, both integral and peripheral which act as either: transporters, linkers, receptors or enzymes.
The lipids within the bilayer can freely move, they can diffuse laterally along the membrane, or rotate along their axis. They are said to be fluid within the system.This fluidity is dependent on:
- the length of the phospholipid tail
- whether the tail is saturated or not
- the presence of cholesterol.<span id="fck_dom_range_temp_1294599428312_305" />
- the glycocalyx
- more about proteins