LIPIDS - CONTINUED

Lipids have much more Carbon than Oxygen and because of that, they are: 
* Lightweight - Oxygen weighs 16 amu's whereas Carbon weighs 12 and Hydrogen only 1.
* Higher Energy Level - 1 gram of lipid has almost twice the number of calories as 1 gram of Carbohydrate

This is a significant adaptation because organisms use Lipids as long-term energy and they are the last energy compound to come out of storage.  So their light weight and high energy yield allows us to survive better and longer.

STRUCTURE OF A TRIGLYCERIDE (most common form of fat)

So, notice that the head (Glycerol) has a chain of 3 Carbons and more closely resembles a sugar while the 3 tails (fatty acids) have very little Oxygen and this is why they're lightweight.  This is a SATURATED FAT because there are no double bonds in the carbon chains of the fatty acids.  MONOUNSATURATED FATS - have one double bond in the chain (missing 2 hydrogens) and POLYUNSATURATED FATS - have 2 or more double bonds and have even less Hydrogens.  The more hydrogens the "straighter" the molecule and so they "stack" in your arteries more easily causing cardiovascular disease.