Amino Acid Explorer

The 20 standard amino acids in 3D. Isolate each R group, compare side chain classes, and learn the pKa, pI, and codon facts the MCAT tests.

Glycine

Gly · G · C₂H₅NO₂

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Side chain

A single hydrogen atom. No side chain proper.

-H

Identity

CodesGly · G
FormulaC₂H₅NO₂
Molecular weight75.07 g/mol
Residue mass57.05 Da
ClassNonpolar
EssentialityConditionally essential

Ionization

alpha-COOHpKa 2.34
alpha-NH3+pKa 9.60
Isoelectric point (pI)5.97
Charge at pH 7Neutral (0)

pI averages the two pKa values that bracket the neutral species - here pKa1 and pKa2. Values are for the free amino acid; they shift inside a folded protein.

Hydropathy

Kyte-Doolittle-0.4
hydrophilichydrophobic

Stereochemistry

Alpha carbonAchiral

The only achiral amino acid. Its alpha carbon carries two hydrogens, so it has no stereocenter and is neither D nor L.

Genetic code

GGUGGCGGAGGG

4 codons

Features

AchiralHelix breaker

MCAT notes

  • The smallest amino acid and the only achiral one - its alpha carbon bears two hydrogens.
  • Maximum conformational freedom (widest allowed Ramachandran region), so it breaks helices by flexibility and is essential at tight turns.
  • Every third residue in collagen (Gly-X-Y, X often Pro, Y often hydroxyproline) because only glycine fits inside the triple helix core.
  • An inhibitory neurotransmitter in the spinal cord, and a co-agonist at NMDA receptors.

G for Glycine, the one with nothing on it.