Amino Acids Reference Chart

Hydrophobic - aliphatic Hydrophobic - aromatic Neutral - polar side chains

Acidic Basic Unique

Properties Table Hydrophobicity Index

Amino acids are the compounds or building blocks that make up peptides and proteins. Each amino acid is structured from an amino group and a carboxyl group bound to a tetrahedral carbon. This carbon is designated as the α-carbon (alpha-carbon).

Amino acids differ from each other with respect to their side chains, which are referred to as R groups. The R group for each of the amino acids will differ in structure, electrical charge, and polarity.

Refer to the charts and structures below to explore amino acid properties, types, applications, and availability.

Amino Acids with Hydrophobic Side Chain – Aliphatic

Alanine, Ala, A

Isoleucine, Ile, I

Leucine, Leu, L

Methionine, Met, M

Valine, Val, V

Amino Acids with Hydrophobic Side Chain – Aromatic

Phenylalanine, Phe, F

Tryptophan, Trp, W

Tyrosine, Tyr, Y

Amino Acids with Polar Neutral Side Chains

Asparagine, Asn, N

Cysteine, Cys, C

Glutamine, Gln, Q

Serine, Ser, S

Threonine, Thr, T

Amino Acids with Electrically Charged Side Chains – Acidic

Aspartic acid, Asp, D

Glutamic acid, Glu, E

Amino Acids with Electrically Charged Side Chains – Basic

Arginine, Arg, R

Histidine, His, H

Lysine, Lys, K

Unique Amino Acids

Glycine, Gly, G

Proline, Pro, P

Properties of Common Amino Acids

Name	Abbr		Molecular Weight	Molecular Formula	Residue Formula	Residue Weight (-H2O)	pKa1	pKb2	pKx3	pl4
Alanine	Ala	A	89.10	C3H7NO2	C3H5NO	71.08	2.34	9.69	–	6.00
Arginine	Arg	R	174.20	C6H14N4O2	C6H12N4O	156.19	2.17	9.04	12.48	10.76
Asparagine	Asn	N	132.12	C4H8N2O3	C4H6N2O2	114.11	2.02	8.80	–	5.41
Aspartic acid	Asp	D	133.11	C4H7NO4	C4H5NO3	115.09	1.88	9.60	3.65	2.77
Cysteine	Cys	C	121.16	C3H7NO2S	C3H5NOS	103.15	1.96	10.28	8.18	5.07
Glutamic acid	Glu	E	147.13	C5H9NO4	C5H7NO3	129.12	2.19	9.67	4.25	3.22
Glutamine	Gln	Q	146.15	C5H10N2O3	C5H8N2O2	128.13	2.17	9.13	–	5.65
Glycine	Gly	G	75.07	C2H5NO2	C2H3NO	57.05	2.34	9.60	–	5.97
Histidine	His	H	155.16	C6H9N3O2	C6H7N3O	137.14	1.82	9.17	6.00	7.59
Hydroxyproline	Hyp	O	131.13	C5H9NO3	C5H7NO2	113.11	1.82	9.65	–	–
Isoleucine	Ile	I	131.18	C6H13NO2	C6H11NO	113.16	2.36	9.60	–	6.02
Leucine	Leu	L	131.18	C6H13NO2	C6H11NO	113.16	2.36	9.60	–	5.98
Lysine	Lys	K	146.19	C6H14N2O2	C6H12N2O	128.18	2.18	8.95	10.53	9.74
Methionine	Met	M	149.21	C5H11NO2S	C5H9NOS	131.20	2.28	9.21	–	5.74
Phenylalanine	Phe	F	165.19	C9H11NO2	C9H9NO	147.18	1.83	9.13	–	5.48
Proline	Pro	P	115.13	C5H9NO2	C5H7NO	97.12	1.99	10.60	–	6.30
Pyroglutamatic	Glp	U	139.11	C5H7NO3	C5H5NO2	121.09	–	–	–	5.68
Serine	Ser	S	105.09	C3H7NO3	C3H5NO2	87.08	2.21	9.15	–	5.68
Threonine	Thr	T	119.12	C4H9NO3	C4H7NO2	101.11	2.09	9.10	–	5.60
Tryptophan	Trp	W	204.23	C11H12N2O2	C11H10N2O	186.22	2.83	9.39	–	5.89
Tyrosine	Tyr	Y	181.19	C9H11NO3	C9H9NO2	163.18	2.20	9.11	10.07	5.66
Valine	Val	V	117.15	C5H11NO2	C5H9NO	99.13	2.32	9.62	–	5.96

¹ pKa is the negative of the logarithm of the dissociation constant for the -COOH group.
² pKb is the negative of the logarithm of the dissociation constant for the -NH3 group.
³ pKx is the negative of the logarithm of the dissociation constant for any other group in the molecule.
⁴ pl is the pH at the isoelectric point.
Reference: D.R. Lide, Handbook of Chemistry and Physics, 72nd Edition, CRC Press, Boca Raton, FL, 1991.

Hydrophobicity Index for Common Amino Acids

The hydrophobicity index is a measure of the relative hydrophobicity, or how soluble an amino acid is in water. In a protein, hydrophobic amino acids are likely to be found in the interior, whereas hydrophilic amino acids are likely to be in contact with the aqueous environment.

The values in the table below are normalized so that the most hydrophobic residue is given a value of 100 relative to glycine, which is considered neutral (0 value). The scales were extrapolated to residues which are more hydrophilic than glycine.

At pH 2A		At pH 7B
Very Hydrophobic
Leu	100	Phe	100
Ile	100	Ile	99
Phe	92	Trp	97
Trp	84	Leu	97
Val	79	Val	76
Met	74	Met	74
Hydrophobic
Cys	52	Tyr	63
Tyr	49	Cys	49
Ala	47	Ala	41
Neutral
Thr	13	Thr	13
Glu	8	His	8
Gly	0	Gly	0
Ser	-7	Ser	-5
Gln	-18	Gln	-10
Asp	-18
Hydrophilic
Arg	-26	Arg	-14
Lys	-37	Lys	-23
Asn	-41	Asn	-28
His	-42	Glu	-31
Pro	-46	Pro	-46 (used pH 2)
		Asp	-55

^ApH 2 values: Normalized from Sereda et al., J. Chrom. 676: 139-153 (1994).
^BpH 7 values: Monera et al., J. Protein Sci. 1: 319-329 (1995).

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