What Are the 21 Amino Acids?

Reviewed on 5/12/2021
amino acids
Out of the 21 amino acids, only 9 are categorized as essential

Amino acids are the basic building blocks of proteins, the compounds that synthesize hormones and neurotransmitters in our bodies. Amino acids help our bodies to grow, repair body tissue, maintain immunity and produce hormones that maintain body functions.

The 21 amino acids different amino acids our bodies need are:

  1. Alanine
  2. Arginine
  3. Asparagine
  4. Aspartic acid
  5. Cysteine
  6. Glutamic acid
  7. Glutamine
  8. Glycine
  9. Histidine
  10. Isoleucine
  11. Leucine
  12. Lysine
  13. Methionine
  14. Phenylalanine
  15. Proline
  16. Serine
  17. Threonine
  18. Tryptophan
  19. Tyrosine
  20. Valine
  21. Selenocysteine

What are the 9 essential amino acids?

Although all of the amino acids are important for our bodies to function properly, only nine of them are classified as essential: 

  1. Phenylalanine
  2. Valine
  3. Tryptophan
  4. Threonine
  5. Isoleucine
  6. Methionine
  7. Histidine
  8. Leucine
  9. Lysine

What are the functions of the 9 essential amino acids?

The 9 essential amino acids play important roles in the body:


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How are amino acids classified?

Amino acids are classified as essential, nonessential and conditionally essential:

  • Essential amino acids: Essential amino acids cannot be made by the body; they must be obtained from the diet.
  • Nonessential amino acids: Nonessential amino acids are produced by the body naturally, although they can also be additionally obtained from food. Nonessential amino acids include:
    • Alanine
    • Arginine
    • Asparagine
    • Aspartic acid
    • Cysteine
    • Glutamic acid
    • Glutamine
    • Glycine
    • Proline
    • Serine
    • Tyrosine
  • Conditionally essential amino acids: Conditionally essential amino acids are ones that your body can’t produce under specific circumstances such as stress or illness. Conditional amino acids include:
    • Arginine
    • Cysteine
    • Glutamine
    • Tyrosine
    • Glycine
    • Ornithine
    • Proline
    • Serine

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Lopez MJ, Mohiuddin SS. Biochemistry, Essential Amino Acids. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK557845/

Medline Plus. Amino Acids. https://medlineplus.gov/ency/article/002222.htm

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