Like all other cellular membranes, the plasma membrane consists of both lipids and proteins. The fundamental structure of the membrane is the phospholipid bilayer, which forms a stable barrier between two aqueous compartments. In the case of the plasma membrane, these compartments are the inside and the outside of the cell.

1. Channel Proteins - form small openings for molecules to difuse through 2. Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell, (gated channels) 3. Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins) 4.