From Shereen Jegtvig,
Your Guide to Nutrition.
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A. The side chain is the part of an amino acid's chemistry that differentiates it from other amino acids. Amino acid structure includes a carboxyl group, an amine group plus the individual side chain. The carboxyl group is made up of one carbon atom, two oxygen atom, and one hydrogen atom. The amine group is made up of nitrogen and hydrogen atoms.

Each amino acid has a unique side chain. The simplest side chain is just one carbon atom with three hydrogen atoms and this side chain belongs to alanine. Some side chains contain sulfur, some contain nitrogen, some are branched and some are ring-shaped. About's Chemistry guide has more information about the chemical structure of amino acids.

Amino acids are the building blocks of protein and you get protein from your diet. If you eat a variety of healthy protein-containing foods, you will get all of the eight essential amino acids that your body can't make for itself, so you really don't have to worry about the individual amino acids.

Sometimes individual amino acids are used therapeutically. For example, tryptophan is used to help treat depression and mood disorders and arginine is effective for lowering high blood pressure.

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