Classes of Amino Acids

Protein from soybeans provides all the amino acids you need.

Protein from soybeans provides all the amino acids you need.

Proteins perform most of your body's functions. The building blocks of proteins are molecules called amino acids, of which there are 20. During protein construction in your cells, amino acids join together as long chains that wrap and twist around each other and give shape to the structure. Each amino acid differs from the others by its chemical properties.

Amino Acid Classes

Two methods define classes of amino acid. The simplest method relates to whether you can make the amino acid on your own—the non-essentials—or whether you must consume the amino acid as part of your diet—the essentials. Some non-essential amino acids become essential during times of illness or stress, and these are called “conditional.” A more complex method of classification depends on the chemical composition of the molecule. Every amino acid has the same chemical backbone comprised of carbon, oxygen, nitrogen and hydrogen. But each of the 20 individual amino acids has a unique character that can play a role in the protein structure or function.

Dietary Classification

Your liver synthesizes some amino acids from atoms that arise from the metabolism of glucose and the breakdown of old proteins in your system. These non-essential amino acids are alanine, asparagine, aspartic acid and glutamic acid. Your diet or supplements must provide ten essential amino acids—arginine, isoleucine, histidine, leucine, methionine, lysine, phenylalanine, tryptophan, threonine and valine. The remaining seven conditional amino acids are arginine, cysteine, glutamine, tyrosine, glycine, proline and serine.

Non-polar Classification

Non-polar amino acids are hydrophobic, or water-hating. They tend to locate in the inner core of the three-dimensional protein, away from the watery cellular environment. This class of amino acids includes isoleucine, valine, phenylalanine, leucine, alanine, methionine, tryptophan, proline and glycine. They most commonly affect the shape of the protein.

Charged Classification

Amino acids with a positive or negative charge are hydrophilic, or water-loving. They tend to locate on the surface of the protein. Because of their ionic character and availability to the cellular environment, these amino acids take part in enzyme activity and other chemical reactions. This class includes histidine, lysine, arginine, aspartic acid and glutamic acid.

Polar Classification

Polar amino acids have a strong ability to take part in biochemical reactions. They regulate the protein’s behavior in the changing environment of the cell. This class contains cysteine, serine, threonine, tyrosine, asparagine and glutamine.


You can find non-essential, essential and conditional amino acids in meat, poultry, milk, cheese, fish, legumes, seeds and nuts. Where diet is not sufficient, you can use supplements. Because you cannot absolutely predict the amino acids your body needs, variety, balance and moderation are vital to providing the most healthful supply of protein building blocks.

About the Author

Susan Miller has been writing since 1970. She has published articles in print journals and online sites, including "Mutation Research" and "Toxicological Sciences." Miller holds a bachelor's degree in chemistry from the University of Florida, as well as a master's degree in biochemistry and a Ph.D. in cell biology from Texas A&M University.

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