Interactive Reference

Periodic Chart of Amino Acids

All 20 standard amino acids, arranged by chemical family. Hover for quick data, click to explore the full story.

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AspD
133.10115.09
C₄H₇NO₄
Aspartic Acid
pKa: 1.99 · 9.90 · 3.90 | pI 2.98
GAT, GAC
Aspartic AcidNamed from asparagus. Key player in the urea cycle and found in licorice-like compounds.
Periodic Chart of Amino Acids
Acidic
Basic
Polar, uncharged
Nonpolar, hydrophobic
HisH
155.16137.14
C₆H₉N₃O₂
Histidine
pKa: 1.80 · 9.33 · 6.04 | pI 7.64
CAT, CAC
HistidineEssential in infants. Its imidazole ring acts as a biological pH sensor near physiological pH.
GluE
147.13129.11
C₅H₉NO₄
Glutamic Acid
pKa: 2.10 · 9.47 · 4.07 | pI 3.08
GAA, GAG
Glutamic AcidThe secret of umami. Its salt (MSG) was isolated from seaweed in 1908. Most abundant AA in nature.
ProP
115.1397.13
C₅H₉NO₂
Proline
pKa: 1.95 · 10.64 | pI 6.30
CCT, CCC, CCA, CCG
ProlineThe only amino acid whose side chain connects back to the nitrogen. Creates kinks in protein chains — crucial for collagen's structure.
GlyG
75.0757.05
C₂H₅NO₂
Glycine
pKa: 2.35 · 9.78 | pI 6.06
GGT, GGC, GGA, GGG
GlycineSmallest and only achiral amino acid. Found in a comet by NASA. Has a sweet taste — named from Greek for "sweet."
CysC
121.16103.14
C₃H₇NO₂S
Cysteine
pKa: 1.92 · 10.70 · 8.37 | pI 5.15
TGT, TGC
CysteineThe disulfide-bond builder. Named from a bladder stone. Why hair is curly or straight depends on its S–S bonds.
ThrT
119.12101.10
C₄H₉NO₃
Threonine
pKa: 2.09 · 9.10 | pI 5.60
ACT, ACC, ACA, ACG
ThreonineLast of the 20 standard amino acids to be discovered (1935). Named after threose sugar because of structural similarity.
ArgR
174.20156.19
C₆H₁₄N₄O₂
Arginine
pKa: 1.82 · 8.99 · 12.48 | pI 10.76
CGT, CGC, CGA, CGG, AGA, AGG
ArginineNamed after silver (argentum) because of its silver salt crystals. Precursor to nitric oxide, essential for blood vessel dilation.
MetM
149.21131.20
C₅H₁₁NO₂S
Methionine
pKa: 2.13 · 9.28 | pI 5.71
ATG
MethionineThe universal "start" codon — every protein synthesis begins here. One of two sulfur-containing amino acids.
TrpW
204.23186.21
C₁₁H₁₂N₂O₂
Tryptophan
pKa: 2.46 · 9.41 | pI 5.88
TGG
TryptophanLargest standard amino acid. One codon only (TGG). The turkey-sleepiness myth is false — most proteins have equal amounts.
ValV
117.1599.13
C₅H₁₁NO₂
Valine
pKa: 2.29 · 9.74 | pI 6.02
GTT, GTC, GTA, GTG
ValineNamed after valerian plant, where it was isolated. A branched-chain amino acid abundant in animal proteins.
AsnN
132.12114.10
C₄H₈N₂O₃
Asparagine
pKa: 2.14 · 8.72 | pI 5.43
AAT, AAC
AsparagineFirst amino acid ever isolated (1806), from asparagus juice. Also responsible for the "asparagus pee" phenomenon.
TyrY
181.19163.17
C₉H₁₁NO₃
Tyrosine
pKa: 2.20 · 9.21 · 10.46 | pI 5.63
TAT, TAC
TyrosineNamed from Greek "tyros" (cheese). A precursor to many critical molecules including melanin (skin pigment) and adrenaline.
LysK
146.19128.17
C₆H₁₄N₂O₂
Lysine
pKa: 2.16 · 9.06 · 10.54 | pI 9.47
AAA, AAG
LysineDiscovered 1889. Its deficiency in corn-based diets caused pellagra epidemics. High in legumes and meat.
LeuL
131.18113.16
C₆H₁₃NO₂
Leucine
pKa: 2.33 · 9.74 | pI 6.04
CTT, CTC, CTA, CTG, TTA, TTG
LeucineNamed from Greek "leukos" (white) for its white crystals. Most common amino acid in proteins — appears in 6 codons.
IleI
131.18113.16
C₆H₁₃NO₂
Isoleucine
pKa: 2.32 · 9.76 | pI 6.04
ATT, ATC, ATA
IsoleucineSame formula as Leucine but different structure. Has two chiral centers — so actually 4 possible stereocenters exist.
AlaA
89.0971.08
C₃H₇NO₂
Alanine
pKa: 2.35 · 9.87 | pI 6.11
GCT, GCC, GCA, GCG
AlanineSecond simplest amino acid, isolated in 1875. Its name comes from "aldehyde" — it was synthesized before it was found in nature.
PheF
165.19147.18
C₉H₁₁NO₂
Phenylalanine
pKa: 2.20 · 9.31 | pI 5.48
TTT, TTC
PhenylalanineThe "PKU amino acid" — its buildup causes phenylketonuria. Also the precursor to tyrosine, dopamine, and adrenaline.
SerS
105.0987.08
C₃H₇NO₃
Serine
pKa: 2.19 · 9.21 | pI 5.70
TCT, TCC, TCA, TCG, AGT, AGC
SerineNamed from Latin "sericum" (silk). Found in silk proteins. Crucial for many enzymes because its –OH group is highly reactive.
GlnQ
146.15128.13
C₅H₁₀N₂O₃
Glutamine
pKa: 2.17 · 9.13 | pI 5.65
CAA, CAG
GlutamineMost abundant free amino acid in human blood. The nitrogen shuttle — carries ammonia between organs without toxicity.

Understanding the Four Families

Acidic (2)

Aspartic acid and Glutamic acid carry a negative charge at physiological pH. Glutamate is famously responsible for umami flavor. Both are key players in energy metabolism and the citric acid cycle.

Basic (3)

Histidine, Arginine, and Lysine carry positive charges and strongly bind to negatively charged DNA — which is why histones (proteins that package DNA) are so rich in these amino acids.

Polar, Uncharged (7)

These amino acids have polar side chains that interact with water but don't carry a full charge. Cysteine is uniquely able to form strong disulfide (S–S) bonds with other cysteines, locking protein structures in place.

Nonpolar, Hydrophobic (8)

These amino acids avoid water and cluster together in the interior of proteins. They're the structural backbone of most enzymes. Tryptophan, the largest, has a complex bicyclic indole ring unique in biology.

Quick Reference: All 20 Standard Amino Acids

Name3-Letter1-LetterCategoryFormulaMol. WeightCodons
AlanineAlaANonpolarC₃H₇NO₂89.09GCT, GCC, GCA, GCG
ArginineArgRBasicC₆H₁₄N₄O₂174.20CGT, CGC, CGA, CGG, AGA, AGG
AsparagineAsnNPolarC₄H₈N₂O₃132.12AAT, AAC
Aspartic AcidAspDAcidicC₄H₇NO₄133.10GAT, GAC
CysteineCysCPolarC₃H₇NO₂S121.16TGT, TGC
Glutamic AcidGluEAcidicC₅H₉NO₄147.13GAA, GAG
GlutamineGlnQPolarC₅H₁₀N₂O₃146.15CAA, CAG
GlycineGlyGPolarC₂H₅NO₂75.07GGT, GGC, GGA, GGG
HistidineHisHBasicC₆H₉N₃O₂155.16CAT, CAC
IsoleucineIleINonpolarC₆H₁₃NO₂131.18ATT, ATC, ATA
LeucineLeuLNonpolarC₆H₁₃NO₂131.18CTT, CTC, CTA, CTG, TTA, TTG
LysineLysKBasicC₆H₁₄N₂O₂146.19AAA, AAG
MethionineMetMNonpolarC₅H₁₁NO₂S149.21ATG
PhenylalaninePheFNonpolarC₉H₁₁NO₂165.19TTT, TTC
ProlineProPNonpolarC₅H₉NO₂115.13CCT, CCC, CCA, CCG
SerineSerSPolarC₃H₇NO₃105.09TCT, TCC, TCA, TCG, AGT, AGC
ThreonineThrTPolarC₄H₉NO₃119.12ACT, ACC, ACA, ACG
TryptophanTrpWNonpolarC₁₁H₁₂N₂O₂204.23TGG
TyrosineTyrYPolarC₉H₁₁NO₃181.19TAT, TAC
ValineValVNonpolarC₅H₁₁NO₂117.15GTT, GTC, GTA, GTG