Triglycerides are lipids made with three fatty acids and a glycerol molecule.
Glycerol. Glycerol (or glycerin) is a three carbon alcohol with a hydroxyl (OH) group coming from each carbon. The fatty acids are joined to the glycerol by a dehydration synthesis is shown in the diagram here.
This tri-glyceride has three saturated fatty acids.
Fats vs oils. Tri-glycerides with unsaturated fatty acids are termed 'oils' in every day speech because they are liquid at room temperature. Tri-glycerides with saturated fatty acids tend to have a higher melting point and are solid at room temperature. We typically call these fats.
Note: oil that comes out of the ground is basically a series of hydrocarbons, not tri-glycerides, so don't confuse these different uses of the word oil!
The difference in physical properties of fats and oils is due to the nature of saturated vs unsaturated bonds in the carbon skeleton of the fatty acids.
Saturated tri-glycerides are considered bad because they cause the body to produce excess cholesterol.
Diagram illustrating the concept of saturated vs. unsaturated bonds. Saturated bonds are when each of the carbons has four single bonds as in the top figure. Unsaturated carbons have one or more double or triple bonds. Note the kinky or pleated shape of the unsaturated carbon skeleton. This spaces the chains allowing them to slide around. This is the main reason unsaturated tri-glycerides tend to liquid at room temperatures: That is, oils rather than fats.
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pgd. revised 7/15//99