The Cell Membrane

1
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  fatty acid chains has been replaced by a very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

2
Phospholipids Water

• 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.

3
The Lipid Bilayer

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

4
More Membrane Components

• 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)

5
The Fluid Mosaic Model

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