Butter, lard, margarine, and salad oil are composed of lipids called fats. To make a fat molecule, three fatty acids bind to a molecule of glycerol. For this reason, fat molecules are technically called triglycerides.
Fat molecules do not mix with water because they have three long nonpolar hydrocarbon tails.
Cells use fats for energy storage because the tails hold more potential energy than other biological molecules. The fatty acid tails in a fat can vary in length. A very important characteristic of fats is the number of double bonds in the hydrocarbon tails.
Fats that contain only single bonds are called saturated fats. Fats containing double bonds in one or more tails are called unsaturated fats. Unsaturated fats tend to be liquid at room temperature.
Vegetable oils are examples.
Saturated fats like butter and lard are solid at room temperature. Saturated fats in the diet can lead to heart disease, whereas unsaturated fats are safer.
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