We survive at the mercy of our lipid bilayer- Cell Membrane

The Cell Membrane All cells are separated from the external environment by a Cell MembraneAll cells are separated from the external environment by a Cell Membrane Membrane is a semipermiable membrane that allows certain materials in/out of cells. Membrane is a semipermiable membrane that allows certain materials in/out of cells. It is composed of many components.It is composed of many components. –Phospholipids –Cholesterol –Proteins Phospholipids Phospholipids –Very similar to triglycerides (glycerol and lipid)

HYDROPHILLIC This is a simple representation of a phospholipid. the yellow structure represents the HYDROPHILLIC or water loving section of the phospholipids. HYDROPHOBIC The blue tails that come off of the sphere represent the HYDROPHOBIC or water fearing end of the Phospholipids.

Phospholipids & Water This poses a problem for the molecule since the molecule is both polar and non-polar simultaneously.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.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..This forces the phospholipids to take an arrangement such that their tails face each other. This accomplishes 2 things.. –The polar heads can be near polar water molecules –The non-polar tails can be near each other.

The Lipid Bilayer As the layer enlarges it forms a bubble shape formed of a lipid bilayer which is the foundation of the cell membraneAs the layer enlarges it forms a bubble shape formed of a lipid bilayer which is the foundation of the cell membrane

Head- polar, phosphorus, philic (loves water) Tail, non polar, lipid, phobic,(repels water)

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

The Fluid Mosaic Model Entire model is referred to as the Fluid Mosaic model of the plasma membraneEntire model is referred to as the Fluid Mosaic model of the plasma membrane