Structure of a cell membrane

• This is a phospholipids bilayer.
• They Hydrophobic tails of the Phospholipid face inward
• The hydrophilic heads of the Phospholipid face outwards
• Within this bilayer are proteins (which may function as enzymes, or carrier and channel proteins)
  
• Many of the proteins have a carbohydrate attached to them which protrudes beyond the outer surface of the membrane. These are called Glycoproteins and are often markers for cell to cell recognition or receptors for hormones and signal proteins.
  
• Some lipids have a carbohydrate attached in the same way and are called Glycolipids
  
• Some proteins span both phospholipid layers and are called integral proteins (intrinsic)
  
• Some proteins are found only in either the outer or inner phospholipid layers and are more easily removed from the membrane. These are called peripheral proteins (extrinsic)

• This is called the fluid mosaic model for membrane structure. Many of the proteins are able to move horizontally within the phospholipid layers (fluid).
  
• Cholesterol is an important component of membranes. It prevents movement of phosolipid molecules so that the membrane is not too fluid.
  

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