Structure of cell membranes

• Cell membranes are partially permeable barriers- they separate the cell's contents from its external environment.
• They need to allow some molecules into or out of the cell.
• Some organelles in the cell have membranes that are barriers too.

PERMEABILITY = The ability to let substances through

• Some very small molecules simply diffuse through the cell; some dissolve in the bilayer and pass through; others pass through protein channels or are carried by carrier proteins

The role of membranes

At the surface of cells:

The plasma membrane:

• Separates the cell's components from its external environment
• Regulates transport of materials into and out of the cell
• May contain enzymes
• Has antigens, so that the cell's immune system can recognise foreign antigens as 'non-self'
• Contains receptors for cell signalling

Within cells:

• The…