Important Terminology:

lipid, hydrocarbon, fat, phospholipid, steroid, triglyceride, saturated fatty acid, unsaturated fatty acid, amphipathic

What is a lipid?

- compounds that typically have little or no attraction for water (What is our term for this?)
- they are typically composed of MOSTLY carbon and hydrogen. They can be distinguished from carbohydrates because their atoms do not appear in any type of ratio to one another. (Remember, C6H12O6. Even disaccharides contain C,H,O in an almost even ratio.)

Three Types of Lipids:

1. Fats (Triacylglycerides, Triglycerides):

  • Fats are composed of a glycerol molecule and three fatty acid chains
  • Glycerol is a molecule with three carbons in a row, each with a hydroxide group (We know what that is!)
  • Fatty acid chains are hydrocarbons- that is, they are composed of mosly carbons and hydrogens. This is a molecule that is VERY hydrophobic.
  • When glycerol combines with the fatty acid chains it forms a carboxyl group between them (We know what that is!) They link by the loss of a water molecule.
external image TRIGLYCERIDE.gif
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external image fat.jpg
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  • Trigylcerides can be solid or liquid at room temperature. Think butter vs. olive oil. This feature is based on whether the fatty acids are saturated or unsaturated. Keep in mind, carbon can bond to four different substances, but sometimes it will share more than one pair of electrons.

2. Phospholipids:

  • Phospholipids are the major component of cell membranes. Their structure helps control what moves into and out of the cell.
  • This type of lipid is amphipathic. What does this mean? (The prefix 'amphi-' means "having both kinds".)
  • Notice in the picture below that the third carbon on the glycerol does not have a fatty acid chain, but instead is attached to a phosphate group.
external image phospholipid_structure.jpg
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3. Steriods:

  • Composed of carbon "skeletons" or rings (at least four)
  • Cholesterol is the most abundant steroid and many other steroids are manufactured from cholesterol: great link on "good" and "bad" cholesterol:
  • Cholesterol is a necessary component of cell membranes to maintain a particular level of fluidity based on the external environment.


Cholesterol and related lipids: Cholesterol and Related Lipids l