Don't memorize names — learn to instantly categorize. 'Glutamic acid' should trigger: negatively charged, acidic, pKa 4.25, Glu, E, hydrophilic, surface residue, salt bridges.
The Four Groups
Nonpolar / Hydrophobic (9)
G A V L I P F W M — mnemonic: 'Grandma Always Visits London In Lovely Pale Fur Weather.' Buried in protein interior. Key: Gly (achiral), Pro (cyclic helix breaker), Met (start codon), Trp (largest, UV 280nm).
Polar Uncharged (6)
S T C Y N Q — 'Santa's Team Creates Your New Quilts.' H-bond donors on protein surface. Key: Cys (disulfide bonds), Tyr (phosphorylation + UV), Asn (N-glycosylation site), Ser/Thr (phosphorylation).
Negatively Charged (2)
D E — Asp (pKa 3.65) and Glu (pKa 4.25). Side chain –COO⁻ at pH 7.4 = −1 each.
Positively Charged (3)
K R H — Lys (pKa 10.53), Arg (pKa 12.48), His (pKa 6.0). +1 at pH 7.4. His is the exam favorite — switches charge near physiological pH.
Special Properties
Achiral: Gly. Disulfide bonds: Cys. UV 280nm: Trp>Tyr>Phe. Phosphorylation: Ser/Thr/Tyr. Two chiral centers: Ile/Thr. Purely ketogenic: Leu/Lys. Essential: PVT TIM HALL.
Calculating Charge at pH
pH < pKa → protonated. pH > pKa → deprotonated. Acidic groups: deprotonation = −1. Basic groups: deprotonation removes +1.
Example: Ala-Asp-Lys at pH 7.4: α-NH₂ (+1) + α-COOH (−1) + Asp (−1) + Lys (+1) = 0