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lipid
A fatlike, nonpolar organic molecule that is insoluble in water (which is a polar molecule) but soluble in nonpolar organic solvents. Lipids include fats, oils, waxes, steroids, phospholipids, and carotenoids.
Lipids are the major fuel reserve for humans and most mammals. These molecules are very efficient at storing needed energy. One gram of fat stores about 9 kcal per gram, compared to carbohydrate or protein (4 kcal per gram). For mobile animals, this means that less bulk has to be carried around and a normal sized body that is about 20% fat has enough stored energy to last about 20-30 days without eating. Fatty foods, with high lipid content, often provide more lipids than can be digested and used right away. The excess is stored in the adipose tissue.
Related entry
• lipid bilayer
Related category
• BIOCHEMISTRY
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