Amino Acids Reference Tool

Alanine is a small, non-essential amino acid with a relatively non-reactive single methyl group side chain. It’s one of the simplest amino acids and the second most abundant in proteins. It’s encoded by codons that start with GC.

Asparagine is an amino acid with a carboxamide side chain. The amide group retains its polarity and is a rich hydrogen bond source, making asparagine a common protein binding site and substrate for glycosyltransferases.

Cysteine is a semi-essential proteinogenic amino acid with a thiol side chain that participates in enzymatic reactions. Its sulfhydryl group forms disulfide bonds with other cysteines or molecules with free sulfhydryls.

Glutamine has a side chain similar to that of glutamic acid; one carboxyl group is simply replaced by an amide. It’s important for nitrogen metabolism and needed to help regulate toxic levels of ammonia in the body.

Histidine is rare and has a partially protonated aromatic imidazole side chain. It may be neutral or positively charged and can serve as a natural catalyst or prevalent residue at enzyme active sites thanks to its bond potential.

Leucine has an isobutyl group side chain with four fully protonated carbons arranged in a bulky "Y" shape. It’s also the most common amino acid in proteins and one of the largest aliphatic amino acids.

Methionine has a linear side chain and contains a sulfide group. This enables methionine to be a prolific methyl group donor. It also plays a critical role in metabolism, the growth of new blood vessels, and tissue repair.

Proline is a proteinogenic amino acid with a cyclic pyrrolidine side chain. It’s non-essential in humans and can be synthesized from glutamic acid. Essential to the immune system, proline is also key to joint and tendon function.

Threonine is an essential amino acid that contains a hydroxyl group, making it polar and uncharged. It shares many properties with serine and is a substrate to kinases and glycosyltransferases. It’s encoded by codons that start with AC.

Tyrosine is an aromatic amino acid similar to phenylalanine with a hydroxyl group instead of a phenyl group in the para position. It has unique chemical properties and serves as a catalyst and substrate for a variety of kinases.

Arginine is a chemically complex amino acid with a 3-carbon aliphatic side chain ending in a guanidino group. It commonly mediates interactions between proteins and negatively charged DNA and RNA backbones.

Aspartic acid has a carboxylic acid side chain that reacts with other amino acids, enzymes, and proteins. Its negative charge and large hydrogen-bonding potential enables its participation in many molecular interactions.

Glutamic acid has one amino and two carboxyl groups that give it a negative charge in virtually all biological systems. This enables glutamic acid to interact with positively charged entities, including metal ions.

Glycine is the simplest amino acid with a single hydrogen atom for a side chain. This makes it ideal for accommodating the tight turns of some polypeptide chains. Glycine also acts as an inhibitory neurotransmitter.

Isoleucine has a branched hydrocarbon side chain arranged in an "L" shape and is considered one of the largest aliphatic amino acids. It’s concentrated in muscle tissue and encoded by the codons AUU, AUC, and AUA.

Lysine is an essential amino acid with a lysyl side chain. It’s important for proteinogenesis, crosslinking collagen polypeptides, absorbing mineral nutrients, and producing carnitine, key for fatty acid metabolism.

Phenylalanine contains a benzyl group side chain and is considered the simplest and most abundant aromatic amino acid in proteins. It’s a precursor for tyrosine synthesis, dopamine, norepinephrine, epinephrine, and melanin.

Serine is an amino acid with a hydroxymethyl group side chain. It’s the simplest hydroxyl amino acid and the third most abundant found in proteins. Serine can be synthesized from glycine and several other metabolites.

Tryptophan is both the largest and rarest amino acid found in proteins. Generally found in the hydrophobic core of proteins, tryptophan is often involved in aromatic stacking. Its side chain is dominated by an indole group.

Valine is a moderately sized aliphatic amino acid with a side chain consisting of a propyl group attached to the CA at C2. Like the other aliphatic residues, valine is often found in the hydrophobic cores of proteins.