All cells Eukaryote (plant and animal), prokaryote (bacteria and blue green algae) contain an outer cell membrane. In addition many of the structures inside of the cell are made up of unit membrane. In this lesson you will learn the chemical makeup and properties of membranes.
 
 
Unit membrane: 
 
 

Membranes of all cells  have the same basic structure.  Membranes consist of a lipid bilayer in
which are embedded globular proteins, many of which extend across the bilayer and protrude on
either side. You may want to go back and review the molecular structure of lipids, and phospholipids which was discussed in miniunit Alpha.
 

 Even though the lipid bilayer provides the basic structure it has an impermeable nature; therefore,  the proteins are responsible for most membrane functions.  Most membranes are composed of 40 to 50 percent lipids and 60 to 50 percent protein.  Not only does the cell membrane consists of unit membrane but many of the cell's organelles consist of unit membrane.

Read the pages indicated by B-4 and study behavioral objectives 2 and 3.

           The figure above represents structures found in a unit membrane. Identify the lipid bilayer (light gray circular structures with two tails hanging in the center), various proteins (these may extend through the lipid bilayer or float on either surface), carbohydrate polymers (these may be attached to lipid molecules - glycolipids or to protein molecules - glycoprotein), cholesterol molecules (indicated by the letter E), cytoskeleton (indicated by F the cytoskeleton are actually protein attachments which extend into the cytoplasm).
 

In your notes draw a figure showing the structure of unit membrane including the following structures: phospholipid bilayer (include the hydrophobic tails and hydrophilic heads), proteins (include both extrinsic and intrinsic), carbohydrates (glycolipid and glycoprotein), cholesterol, pores. The phospholipid layer makes the membrane impervious to water and polar molecules. In your notes explain hydrophilic heads and hydrophobic tails in relation to polar and nonpolar properties. You may want to go back and review nonpolar compounds (lipids) and polar compounds (water) in miniunit alpha.  In your notes fill in the table below indicating  four functions of the cell membrane.
 

       Membrane Function                                                Write how function is accomplished

isolation from environment
transport regulation
communication
identification

 

Click ere to go back to readings in membrane bound organelles. click