Amino Acids

Amino acids are the building blocks (monomers) of proteins. 20 different amino acids are used to synthesize proteins. The shape and other properties of each protein is dictated by the precise sequence of amino acids in it.

Each amino acid consists of an alpha carbon atom to which is attached

The Amino Acids
(For each amino acid, both the three-letter and single-letter codes are given. Click the name to see the structural formula)
ArginineArgRfree amino group makes it basic and hydrophilic
AsparagineAsnNcarbohydrate can be covalently linked ("N-linked) to its -NH
Aspartic acidAspDfree carboxyl group makes it acidic and hydrophilic
CysteineCysCoxidation of their sulfhydryl (-SH) groups link 2 Cys (S-S)
Glutamic acidGluEfree carboxyl group makes it acidic and hydrophilic
GlutamineGlnQmoderately hydrophilic
GlycineGlyGso small it is amphiphilic (can exist in any surroundings)
HistidineHisHbasic and hydrophilic
LysineLysKstrongly basic and hydrophilic
PhenylalaninePheFvery hydrophobic
ProlineProPcauses kinks in the chain
SerineSerScarbohydrate can be covalently linked ("O-linked") to its -OH
ThreonineThrTcarbohydrate can be covalently linked ("O-linked") to its -OH
TryptophanTrpWscarce in most plant proteins
TyrosineTyrYa phosphate or sulfate group can be covalently attached to its -OH

Humans must include adequate amounts of 9 amino acids in their diet. These "essential" amino acids cannot be synthesized from other precursors. However, cysteine can partially meet the need for methionine (they both contain sulfur), and tyrosine can partially substitute for phenylalanine.

The Essential Amino Acids
Methionine (and/or cysteine)
Phenylalanine (and/or tyrosine)

Two of the essential amino acids, lysine and tryptophan, are poorly represented in most plant proteins. Thus strict vegetarians should ensure that their diet contains sufficient amounts of these two amino acids.

19 of the 20 amino acids listed above can exist in two forms in three dimensions. Link to a discussion.

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21 December 2010