Peptide Science
What Is an Amino Acid? The Building Block Behind Every Peptide
Twenty proteinogenic residues, one shared backbone, and side chains that decide charge, solubility and stability. A short structural primer for laboratory work.
August 22, 2026 · 5 min read · Novanta Research
One backbone, twenty side chains
Every proteinogenic amino acid shares the same core: a central carbon bonded to an amino group, a carboxylic acid group, a hydrogen, and a variable side chain. The side chain is the only part that differs, and it is what gives each residue its personality.
Side chains are usually grouped as nonpolar, polar uncharged, acidic, or basic. That grouping predicts most of what a laboratory cares about — whether a sequence dissolves readily in water, how it behaves at a given pH, and which residues are vulnerable to oxidation.
Charge and the isoelectric point
Acidic residues such as aspartate and glutamate carry a negative charge at neutral pH; basic residues such as lysine and arginine carry a positive charge. The pH at which the whole molecule carries no net charge is its isoelectric point, and solubility is usually at its lowest there.
That single fact explains many reconstitution problems. A peptide that refuses to go into plain water often dissolves immediately once the pH is moved away from its isoelectric point with a small amount of dilute acid or base.
Residues that need extra care
Methionine and cysteine oxidise. Cysteine can also form unintended disulfide bridges between chains, which shows up as dimer peaks on a chromatogram. Asparagine and glutamine deamidate over time, especially in solution and at higher pH.
Tryptophan is light sensitive. This is one of the reasons research vials are stored in the dark and reconstituted material is kept away from bench lighting whenever the study design permits.
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For laboratory and research use only. Not for human or veterinary consumption. Novanta Research is not a compounding pharmacy and nothing in this article is medical advice or a claim that any compound diagnoses, treats, cures or prevents any condition.