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Amino Acids are the basic structural building units of proteins. They form short polymer chains called peptides or longer chains called either polypeptides or proteins. An amino acid is a molecule that contains both amino (NH2) and carboxyl (COOH) functional groups.[1]

There are 20 standard amino acids, 8 of which are essential, meaning the body cannot synthesize them from other compounds at the level needed for normal growth, so they must be obtained from food. [2][3] Nonessential amino acids are made by the body from the essential amino acids or normal breakdown of proteins.[1] The amino acids cysteine, tyrosine, histidine and arginine are semiessential amino acids in children, because the metabolic pathways that synthesize these amino acids are not fully developed yet.

Standard Amino Acids[]

Essential Nonessential
Isoleucine Alanine
Leucine Asparagine
Lysine Aspartate
Methionine Cysteine
Phenylalanine Glutamate
Threonine Glutamine
Tryptophan Glycine
Valine Proline

Branched-Chain Amino Acids[]

The term Branched-chain amino acids or BCAAs sometimes refers to the amino acids having aliphatic side-chains that are non-linear. These are leucine, isoleucine and valine. The combination of these three essential amino acids make up approximately 1/3 of skeletal muscle in the human body, and play an important role in protein synthesis. BCAAs are currently used clinically to aid in the recovery of burn victims, as well as for supplementation for strength athletes.[4]


  1. 1.0 1.1
  2. Donche, Dan (2008). FF Trainer Certification Guide. USA: Fatal Fitness. 
  3. Gastelu, Dan; Hatfield, Frederick C (2006). Specialist in Performance Nutrition: The Complete Guide. Carpenteria, CA: ISSA, 17. 
  4. various (n.d.). Branched-chain Amino Acids. Wikipedia. Retrieved on 2008-09-19.
Amino Acids
Amino Acids AlanineArginineAsparagineAspartateCysteineGlutamateGlutamineGlycineHistidineIsoleucineLeucineLysineMethioninePhenylalanineProlineSerineThreonineTryptophanTyrosineValine
Essential Amino Acids IsoleucineLeucineLysineMethioninePhenylalanineThreonineTryptophanValine
Nonessential Amino Acids AlanineArginineAsparagineAspartateCysteineGlutamateGlutamineGlycineHistidineProlineSerineTyrosine
BCAAs IsoleucineLeucineValine