Amino Acid Recall Sheet
Amino Acid Masterclass
Complete Recall Sheet — All 20 Standard Amino Acids
Eightfold Learning
Nonpolar Aliphatic (7)
G A V L I M P
Aromatic (3)
F Y W
Polar Uncharged (5)
S T C N Q
Basic / + Charged (3)
K R H
Acidic / − Charged (2)
D E
💡 Memorization Tips & Mnemonics
1-letter codes: Most abbreviations use the first letter of the name.
Focus on memorizing the exceptions — it is easier than memorizing all 20:
D (Asp), E (Glu), F (Phe), K (Lys), M (Met), N (Asn), Q (Gln), R (Arg), W (Trp), Y (Tyr)
Branched-chain AAs: LIV (Leucine · Isoleucine · Valine)
Phosphorylatable AAs: YST (Tyrosine · Serine · Threonine)
| Name | Structure (α, β, γ labels) | 1 | 3 | Category | Functional Group | Special / MCAT Key Points | IMF / Interactions |
|---|---|---|---|---|---|---|---|
| Nonpolar Aliphatic (7 amino acids) | |||||||
| Glycine | H | G | Gly | Nonpolar Aliphatic | None (H) | Smallest AA; achiral (no chiral center — does not rotate plane-polarized light); greatest backbone flexibility; found in tight turns & active sites | London Dispersion |
| Alanine | βCH3 | A | Ala | Nonpolar Aliphatic | Methyl | Simplest chiral AA; strong α-helix former | London Dispersion |
| Valine | βCH(γCH3)2 | V | Val | Nonpolar Aliphatic | Isopropyl | Branched at Cβ; hydrophobic core packing; Val→Glu mutation causes sickle-cell anemia | London Dispersion |
| Leucine | βCH2—γCH(δCH3)2 | L | Leu | Nonpolar Aliphatic | Isobutyl | Branched at Cγ | London Dispersion |
| Isoleucine | βCH(CH3)—γCH2—δCH3 | I | Ile | Nonpolar Aliphatic | sec-Butyl | Branched at Cβ; 2 chiral centers (Cα & Cβ) | London Dispersion |
| Methionine | βCH2—γCH2—S—CH3 | M | Met | Nonpolar Aliphatic | Thioether (−S−) | Start codon (AUG) | London Dispersion (weak dipole from S) |
| Proline | (ring bonds to α-N) | P | Pro | Nonpolar Aliphatic | Cyclic 2° amine | Only AA with secondary amine (N is in ring); disrupts α-helices & β-sheets; rigid; found in β-turns; collagen has Gly-Pro-Hyp repeats | London Dispersion |
| Aromatic (3 amino acids) | |||||||
| Phenylalanine | βCH2— | F | Phe | Aromatic | Phenyl | Nonpolar aromatic; hydrophobic core | London Dispersion, π–π stacking |
| Tyrosine | βCH2— | Y | Tyr | Aromatic | Phenol (para-OH) | UV absorber; phosphorylatable (−OH) | H-bonding, π–π stacking, London Dispersion |
| Tryptophan | βCH2— | W | Trp | Aromatic | Indole | UV absorber (main contributor) | H-bonding (indole NH), π–π stacking, London Dispersion |
| Polar Uncharged (5 amino acids) | |||||||
| Serine | βCH2—OH | S | Ser | Polar Uncharged | Hydroxyl (−OH) | Phosphorylatable; active site of serine proteases (Ser–His–Asp catalytic triad) | H-bonding (donor & acceptor) |
| Threonine | βCH(OH)—γCH3 | T | Thr | Polar Uncharged | Hydroxyl (−OH) | Phosphorylatable; 2 chiral centers (Cα & Cβ); branched at Cβ; essential AA | H-bonding (donor & acceptor) |
| Cysteine | βCH2—SH | C | Cys | Polar Uncharged | Thiol (−SH) | Disulfide bonds (−S−S−, oxidation of 2 Cys) | H-bonding (weak), London Dispersion, S−S covalent crosslinks |
| Asparagine | βCH2—C(=O)NH2 | N | Asn | Polar Uncharged | Amide | 2C side chain (β-amide) | H-bonding (amide N−H & C=O) |
| Glutamine | βCH2—γCH2—C(=O)NH2 | Q | Gln | Polar Uncharged | Amide | 3C side chain (γ-amide) | H-bonding (amide N−H & C=O) |
| Basic (+) (3 amino acids) | |||||||
| Lysine | βCH2—γCH2—δCH2—εCH2—NH3+ | K | Lys | Basic (+) | ε-Amino (pKa ~10.5) | Positive at pH 7; longest basic chain; found in histones | Ionic (salt bridges), H-bonding |
| Arginine | βCH2—γCH2—δCH2—NH—C(=NH)NH2 | R | Arg | Basic (+) | Guanidinium (pKa ~12.5) | Most basic AA; always + at physiological pH; found in histones | Ionic, H-bonding (multiple) |
| Histidine | βCH2— | H | His | Basic (+) | Imidazole (pKa ~6.0) | Only AA with pKa near physiological pH (~6.0); can be + or neutral near pH 7; active site proton shuttle | H-bonding, Ionic (when protonated) |
| Acidic (-) (2 amino acids) | |||||||
| Aspartate | βCH2—COO− | D | Asp | Acidic (-) | β-Carboxylate (pKa ~4.0) | Negative at pH 7; Asp–His–Ser catalytic triad (serine proteases); 2C side chain (β-carboxylate); phosphomimetic | Ionic (salt bridges), H-bonding |
| Glutamate | βCH2—γCH2—COO− | E | Glu | Acidic (-) | γ-Carboxylate (pKa ~4.0) | Negative at pH 7; major excitatory neurotransmitter; 3C side chain (γ-carboxylate); phosphomimetic | Ionic (salt bridges), H-bonding |
Structure color key:
■ Carboxylate / Acidic
■ Amino / Basic
■ Hydroxyl
■ Sulfur
■ Aromatic ring
■ Amide
β/γ/δ/ε Carbon position label
* All 20 standard amino acids are L-amino acids (except Gly which is achiral).
* pKa values are approximate side-chain values at 25°C.
* “Charge at pH 7” refers to the side chain only (backbone always zwitterionic).
* IMF refers to additional interactions the R-group can participate in.