Amino acids

Overview

Bifunctional molecules containing amino and carboxyl groups.

Amino acids condense to form peptide links and are recovered when peptides and proteins are hydrolysed.

Amino acids contain amino and carboxyl functionality. Many exist mainly as zwitterions in water, with oppositely charged groups in one molecule. Their net charge depends on pH and ionisable side chains. Joining amino acids creates peptide bonds with a sequence and direction, not an interchangeable mixture of residues.

Identifiers

Functional group

NH2 and COOH

Properties

Zwitterion

A species can have zero net charge while containing both positive and negative formal charges.

Stereochemistry

Glycine has no chiral alpha carbon; most common protein amino acids do, and proline has a secondary amino group.

Sequence boundary

Mixing unprotected amino acids does not specify one pure peptide sequence.

Related compounds

• Glycine

  The simplest alpha-amino acid and the achiral exception among common protein amino acids.

• L-Alanine

  A chiral alpha-amino acid with a methyl side chain.

• L-Valine

  L-Valine is an organic compound with the molecular formula C5H11NO2.

• L-Leucine

  L-Leucine is an organic compound with the molecular formula C6H13NO2.

• L-Isoleucine

  L-Isoleucine is an organic compound with the molecular formula C6H13NO2.

• L-Serine

  L-Serine is an organic compound with the molecular formula C3H7NO3.

• L-Threonine

  L-Threonine is an organic compound with the molecular formula C4H9NO3.

• L-Cysteine

  A sulfur-containing amino acid with a thiol side chain.

• L-Methionine

  L-Methionine is an organic compound with the molecular formula C5H11NO2S.

• L-Aspartic acid

  L-Aspartic acid is an organic compound with the molecular formula C4H7NO4.

• L-Glutamic acid

  L-Glutamic acid is an organic compound with the molecular formula C5H9NO4.

• L-Asparagine

  L-Asparagine is an organic compound with the molecular formula C4H8N2O3.

• L-Glutamine

  L-Glutamine is an organic compound with the molecular formula C5H10N2O3.

• L-Lysine

  An amino acid with an additional basic amino group in its side chain.

• L-Arginine

  L-Arginine is an organic compound with the molecular formula C6H14N4O2.

• L-Histidine

  L-Histidine is an organic compound with the molecular formula C6H9N3O2.

• L-Phenylalanine

  L-Phenylalanine is an organic compound with the molecular formula C9H11NO2.

• L-Tyrosine

  L-Tyrosine is an organic compound with the molecular formula C9H11NO3.

• L-Tryptophan

  L-Tryptophan is an organic compound with the molecular formula C11H12N2O2.

• L-Proline

  L-Proline is an organic compound with the molecular formula C5H9NO2.

Connected reactions

• Peptide formation: Amino acids → Peptides and proteins

  Controlled amino-acid coupling forms peptide bonds; the displayed equation is a net relationship rather than a complete experimental procedure.

• Peptide hydrolysis: Peptides and proteins → Amino acids

  Peptide bonds are hydrolysed by prolonged heating with aqueous hydrochloric acid, followed by work-up when free amino acids are required.

References

1. Organic Chemistry: Structures of Amino AcidsJohn McMurry · OpenStax Organic Chemistry · 2023

   Supports functional-group chemistry used to curate the linked examples. Checked 2026-09-16; named examples are applications of textbook scope, without claimed experimental yields.

2. Organic Chemistry: Peptide SynthesisJohn McMurry · OpenStax Organic Chemistry · 2023

   Supports controlled peptide synthesis using amino-acid protection strategies and carbodiimide coupling reagents rather than treating direct amino-acid dehydration as a complete laboratory method.

3. PubChem Compound Summary: Glycine (CID 750)National Center for Biotechnology Information · PubChem

   Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

4. PubChem Compound Summary: L-Alanine (CID 5950)National Center for Biotechnology Information · PubChem

   Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

5. PubChem Compound Summary: L-Valine (CID 6287)National Center for Biotechnology Information · PubChem

   Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

6. PubChem Compound Summary: L-Leucine (CID 6106)National Center for Biotechnology Information · PubChem

   Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

7. PubChem Compound Summary: L-Isoleucine (CID 6306)National Center for Biotechnology Information · PubChem

   Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

8. PubChem Compound Summary: L-Serine (CID 5951)National Center for Biotechnology Information · PubChem

   Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

9. PubChem Compound Summary: L-Threonine (CID 6288)National Center for Biotechnology Information · PubChem

   Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

10. PubChem Compound Summary: L-Cysteine (CID 5862)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

11. PubChem Compound Summary: L-Methionine (CID 6137)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

12. PubChem Compound Summary: L-Aspartic acid (CID 5960)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

13. PubChem Compound Summary: L-Glutamic acid (CID 33032)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

14. PubChem Compound Summary: L-Asparagine (CID 6267)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

15. PubChem Compound Summary: L-Glutamine (CID 5961)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

16. PubChem Compound Summary: L-Lysine (CID 5962)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

17. PubChem Compound Summary: L-Arginine (CID 6322)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

18. PubChem Compound Summary: L-Histidine (CID 6274)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

19. PubChem Compound Summary: L-Phenylalanine (CID 6140)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

20. PubChem Compound Summary: L-Tyrosine (CID 6057)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

21. PubChem Compound Summary: L-Tryptophan (CID 6305)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

22. PubChem Compound Summary: L-Proline (CID 145742)National Center for Biotechnology Information · PubChem

    Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.