Essential amino acid

An essential amino acid for an organism is an amino acid that cannot be synthesized by the organism from other available resources, and therefore must be supplied as part of its diet.

Related Topics:
Amino acid - Organism

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Eight amino acids are generally regarded as essential for humans: tryptophan, lysine, methionine, phenylalanine, threonine, valine, leucine, isoleucine. Two others, histidine and arginine are essential only in children. A good mnemonic device for remembering these is "Private Tim Hall", abbreviated as: PVT TIM HALL.

Related Topics:
Amino acid - Tryptophan - Lysine - Methionine - Phenylalanine - Threonine - Valine - Leucine - Isoleucine - Histidine - Arginine - Mnemonic

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Which amino acids are essential, varies from species to species, as different metabolisms are able to synthesize different substances. For instance, taurine (which is not, by strict definition, an amino acid) is essential for cats, but not for dogs. Thus, dog food is not nutritionally sufficient for cats, and taurine is added to commercial cat food, but not to dog food.

Related Topics:
Taurine - Cat - Dog

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

For example, phenylalanine is an essential amino acid for humans. Alanine can be synthesized from pyruvate in humans.

Related Topics:
Phenylalanine - Alanine - Pyruvate

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Technically, the "20 proteinogenic amino acids" figure is a bit vexing. You also find selenocysteine, a selenium-containing derivate, in a few proteins, adding another one to the score, but according to chemical nomenclature rules, proline, due to its structure, is really an imino acid - its side chain is linked to the backbone at two points forming a ring rather than simply branching off. Thus, there are indeed 20 proteinogenic amino acids, but strictly speaking, two of them are not those that are normally given. Additionally, amino acids can be chemically altered after being incorporated into a protein, but these derivates do not constitute proteinogenic amino acids as they are only created after polymerization of the protein.

Related Topics:
Selenocysteine - Selenium - Proline - Imino acid

~ ~ ~ ~ ~ ~ ~ ~ ~ ~