Amino Acids

Tryptophan, the amino acid with the largest sidechain, seen in EnzDes coloring.

Animation of some arginine sidechain positions.

Alanine, the amino acid with the smallest sidechain, except for glycine, which has no sidechain.

Histidine.

Phenylalanine.

Aspartate, or aspartic acid.

Glutamate, or glutamic acid.

Lysine.

Amino acids (also called segments or residues in Foldit) are the building blocks of proteins. Each amino acid has a unique sidechain, except for glycine.

Each protein is identified by a unique sequence of amino acids, the primary structure of the protein.

The table below shows the 20 amino acids used in Foldit. Clicking on the arrows in the column heads changes the sort order of the table. The table is explained in detail below.

Amino Acid	3-Letter	1-Letter	Hydrophobicity / Hydropathy index	polarity	acidity (pH)
Alanine	Ala	A	1.8	nonpolar	neutral
Arginine	Arg	R	-4.5	polar	basic (strongly)
Asparagine	Asn	N	-3.5	polar	neutral
Aspartate (aspartic acid)	Asp	D	-3.5	polar	acidic
Cysteine	Cys	C	2.5	polar	neutral
Glutamate (glutamic acid)	Glu	E	-3.5	polar	acidic
Glutamine	Gln	Q	-3.5	polar	neutral
Glycine	Gly	G	-0.4	nonpolar	neutral
Histidine	His	H	-3.2	polar	basic (weakly)
Isoleucine	Ile	I	4.5	nonpolar	neutral
Leucine	Leu	L	3.8	nonpolar	neutral
Lysine	Lys	K	-3.9	polar	basic
Methionine	Met	M	1.9	nonpolar	neutral
Phenylalanine	Phe	F	2.8	nonpolar	neutral
Proline	Pro	P	-1.6	nonpolar	neutral
Serine	Ser	S	-0.8	polar	neutral
Threonine	Thr	T	-0.7	polar	neutral
Tryptophan	Trp	W	-0.9	nonpolar	neutral
Tyrosine	Tyr	Y	-1.3	polar	neutral
Valine	Val	V	4.2	nonpolar	neutral

See the amino acid gallery for examples of what each amino acid looks like in Foldit.

See also spmm's amino acid table, which shows the odds of each amino acid being found in helix, sheet, and loop.

See proteinogenic amino acid on wikipedia for more information about each amino acid.

Detail

The table shows how amino acids are identified and lists the key characteristics of their sidechains.

Amino Acid

The first column shows each amino acid's full name, and links to its detail page.

Two amino acids have two names. Aspartate is also called aspartic acid, and glutamate is also called glutamic acid. This is because both have acid sidechains.

3-letter code

Some sources, such as the PDB, use three-letter codes to represent amino acids.

1-letter code

The primary structure of a protein is often reported one-letter codes, such as in FASTA format. Foldit uses lower case for these codes.

Hydrophobicity/Hydropathy index

One important characteristic of an amino acid is how it interacts with water, also known as hydrophobicity. In Foldit, an amino acid is either hydrophilic, meaning it likes water, or hydrophobic, meaning it tries to avoid water. The hydropathy index is a more refined version of this idea.

The hydropathy index values shown in blue are for amino acids classified as hydrophilic in Foldit. The values shown in orange are for amino acids considered hydrophobic. In general, negative values are hydrophilic in Foldit, and positive values are hydrophobic. There are several exceptions in the middle of the table, however.

Polarity

The amino acids listed as "polar" have sidechains with nitrogen or oxygen atoms that can form hydrogen bonds. See sidechain bonding gallery and sidechain bonding table for details on the bondable atoms

Acidity (pH)

The sidechain of each amino acid is classified as acidic, basic, or neutral.