Levels of Organization Image Map
What do we know about the lipids that make membranes?
  • Membranes are thin sheets of fat-like molecules that wrap around cells and also around many parts (organelles) within cells. 
  • Membranes separate the components, either within a cell or among various cells. 
  • The fatty molecules ("lipids") that make up most of a cell  occur in two adjacent layers. 


Lipid Image

The + and - signs in the drawing represent the electrical charge distribution on the end of the lipid. These are usually carried by phosphate (PO4) and carbonyl (CO) groups. In a real cell membrane, the lipid self-organizes into two layers.

Lollipop Lipids

Would you believe that chemists represent lipids with little drawings that look like lollipops? 

  • The circle at one end represents an electrically charged "phosphate group", which is the atom phosphorous bonded to four molecules of oxygen. 

  • These phosphate groups are attracted to water because water is charged (the + pole of water molecules attracts to the negative pole of the phosphate.)

  • The stem of the lollipop represents a chain of carbon atoms that is attached to the phosphate group.

    Most drawings of lipid symbols show two stems, because real lipids have two parallel chains of carbons attached to the phosphate group.
    Lipids line up parallel to each other in the presence of water. In other words, at water's surface, the lipid molecules are "standing on their heads."


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