Cell Membrane

The Cell Membrane

• All  cells are separated from the external environment by a Plasma Membrane
•  Membrane is pliable and semipermiable only allowing certain materials in/out of cells.
• It is composed of many components.
  • Phospholipids
  • Cholsterol
  • Proteins
•  Phospholipids
  • Very similar to triglycerides however, one of the fatty acid chains has been replaced by a very polar Phosphate group

 

• This poses a problem for the molecule since the molecule is both polar and non-polar simultaneously.
• It is therefore very unstable in water, polar end is attracted to it, non polar tails are repelled by it.

• This forces the phospholipids to take an arrangement such that their tails face each other.  This accomplishes 2 things..
  • The polar heads can be adjacent to polar water molecules
  • The non-polar tails can be adjacent to each other.

 

• As the layer enlarges it forms a bubble shape formed of a lipid bilayer which is the foundation of the plasma membrane

 

 

 

• The membrane requires a few more components to make it complete:
• Cholesterol
  • Functions to hold the membrane together like glue.  Adds strength to the membrane.
• Proteins (2 types)
  • Intrinsic Proteins
    • Extend into or through lipid bilayer
    • Often are channel proteins allowing large molecules in/out
  • Extrinsic Proteins
    • Exist only on surfaces of the bilayer
    • Often serve as receptor molecules
    • Glycoproteins serve as cellular markers (nametags)

 

• Entire model is referred to as the Fluid Mosaic model of the plasma membrane