(10) Structure of the cell membrane

     (19) The Bilayer   

    (21) Structure of phospholipids

Cells are the building blocks of life. All the existing living organisms consist of as few as one or as many as trillions of different cells. Cells are responsible for carrying a multitude of vital processes, such as taking in nutrients, expelling waste, and reproducing, that are essential for the proper functioning of our bodies (16).

Every cell is surrounded by a thin, protective layer, called the cell membrane. Although extremely thin, measuring merely 8 nanometres, it is a highly developed and specialized structure (9). The cell membrane acts as a gateway that controls the continuous passage of substances inside and out of the cell; it determines what amounts and types of molecules can enter and leave the cell (10, 12).

The cell membrane is a bilayer that consists of billions of tiny phospholipid and protein molecules (12, 16). Phospholipids are fat derivatives in which one fatty acid has been replaced by a phosphate group and one of several nitrogen-containing molecules (17). They are made up of a phosphate hydrophilic head and a lipid hydrophobic tail (14, 16, 18). Therefore, when placed in water, phospholipids behave like both an insoluble hydrocarbon and a soluble ionic compound – the hydrophobic carbon chains aggregate to exclude water while the hydrophilic part is drawn to water that can solvate it. This results in a spontaneous formation of a spherical double layer of phospholipids that is called a lipid bilayer (13, 14, 15, 20, 22).

   The proteins that are embedded in the cell are responsible of performing various functions. Some act like gate keepers that open and close to control what enters and leaves the cell. Other types, however, act as the receptor sites for hormones (16).