Structure of the plasma membrane
Phospholipid molecule
A phospholipid molecule has: a polar head (includes a phosphate group) Nonpolar tails (fatty acids)
The polar phosphate group A key component of living things is water Water is polar The polar phosphate group allows the cell membrane to interact with its watery environment. (HYDROPHILIC) Like dissolves like!
Nonpolar fatty acid tails The fatty acid tails are nonpolar therefore they avoid water. (HYDOPHOBIC)
Two layers of phospholipid molecules make a sandwich. the phospholipid head face the watery environments found inside and outside the cell. the fatty acid tails form the interior of the membrane.
When many phospholipid molecules come together in this manner, a barrier is created that is water-soluble at its outer surfaces and water-insoluble in the middle. Water-soluble molecules will not easily move through the membrane because they are stopped by the nonpolar fatty acid tails.
Other components of the plasma membrane Transport Proteins –used for transportation of material into and out of the cell. Carbohydrates & proteins – used for chemical signals Cholesterol – help stabilize the phospholipids by preventing their fatty acid tails from sticking together.
Fluid mosaic model This is a term used to describe the plasma membrane because molecules are free to move sideways within a lipid bilayer.