Amino Acid Classification

Asp (Aspartic Acid)

Charged Carboxyl Group (highly negative O → O is highly reactive)

pKa = 3.9 (acidic)

pH = 7 = net negative charge

Glu (Glutamic acid)

Charged Carboxyl Group

pKa = 4.1

pH = 7 = net negative charge

Lys (Lysine)

Charged Amino Group

pKa = 10.5

pH = 7 = net positive charge

Arg (Arginine)

Charged Amino group

pKa = 12.5

pH = 7 = net positive charge

His (Histidine)

Charged → has an imidazole ring

pKa = 6

Either positive charge or negative charge based on environment

Ser (Serine)

Hydrophilic → can hydrogen bond (OH)

No pKa because not charged

MOST likely to be found on surface of proteins

Thr (Threonine)

Hydrophilic → can hydrogen bond (OH)

No pKa because not charged

Cys (Cysteine)

Hydrophilic → sulfur hydrogen reacts with water (H react

Only R-Group with sulfur

pKa = 8.3

Asn (Asparagine)

Hydrophilic → NH2 reacts with water

Found on the surface of globular proteins (circular proteins)

Gln (Glutamine)

Hydrophilic → NH2 reacts with water

Gly (Glycine)

Hydrophobic

R group = H

chemically neutral

Als (Alanine)

Hydrophobic

CH3 = R group

Pro (Proline)

Hydrophobic -→ Cyclic ring limits the conformations that it can adopt

Val (Valine)

Hydrophobic

is the core of globular proteins

Leu (Leucicine)

Hydriphobic

No pKa

Ile (Isoleucine)

Hydrophobic

No pKa

Met (Methionine)

Hydrophobic → no disulfide bonds

No pKa

Phe (Phenylalanine)

Aromatic

No H-bonds present = hydrophobic

Tyr (Tyrosine)

Aromatic

Hydrophilic (OH) and Hydrophobic → AKA Amphipathic

pKa = 10.1

weakly absorb UV light

Trp (Tryptophan)

Aromatic

Hydrophilic (OH) and Hydrophobic → AKA Amphipathic

Strongly absorb UV light