Essential amino acids

Definition

Amino acids that an organism cannot synthesize de novo at rates sufficient to meet metabolic demand and therefore must obtain from dietary protein. The specific set varies by taxon; for example, insects typically require ten essential amino acids (the nine required by mammals plus arginine), while some phytophagous insects obtain symbiotic bacterial assistance to supplement deficits in plant tissues. Dietary limitation of any essential amino acid constrains growth, reproduction, and immune function.

Etymology

From Latin 'essentialis' (fundamental, necessary) + Greek 'amino' (containing ammonia) + 'acid'

Example

The pea aphid Acyrthosiphon pisum relies on its obligate bacterial endosymbiont Buchnera aphidicola to synthesize essential amino acids that are scarce in plant phloem sap, particularly tryptophan and leucine; aphids deprived of this symbiosis cannot complete development.

Synonyms

• indispensable amino acids

Related Terms

• protein quality
• limiting amino acid
• nutritional ecology
• symbiotic nitrogen fixation
• phloem sap
• holometabolous development
• ecdysteroid synthesis
• nitrogen limitation

Usage Notes

The roster of essential amino acids differs markedly across taxa and life stages; what is essential for a vertebrate may be synthesized by an insect or its microbiome. In ecological studies, 'essential' is sometimes used more loosely to mean 'required in the diet under field conditions' rather than 'incapable of synthesis.' Arachnologists and entomologists should verify the specific list for their study organism rather than assuming the human/mammalian set of nine.