amino acid

American  

[uh-mee-noh as-id] / əˈmi noʊ ˈæs ɪd /

noun

Biochemistry.

1. any of a class of organic compounds that contains at least one amino group, –NH 2 , and one carboxyl group, –COOH: the alpha-amino acids, RCH(NH2 )COOH, are the building blocks from which proteins are constructed.

---

amino acid British  

noun

1. any of a group of organic compounds containing one or more amino groups, -NH 2 , and one or more carboxyl groups, -COOH. The alpha-amino acids RCH(NH 2 )COOH (where R is either hydrogen or an organic group) are the component molecules of proteins; some can be synthesized in the body ( nonessential amino acids ) and others cannot and are thus essential components of the diet ( essential amino acids )

---

amino acid Scientific  

1. Any of a large number of compounds found in living cells that contain carbon, oxygen, hydrogen, and nitrogen, and join together to form proteins. Amino acids contain a basic amino group (NH ₂) and an acidic carboxyl group (COOH), both attached to the same carbon atom. Since the carboxyl group has a proton available for binding with the electrons of another atom, and the amino group has electrons available for binding with a proton from another atom, the amino acid behaves as an acid and a base simultaneously. Twenty of the naturally occurring amino acids are the building blocks of proteins, which they form by being connected to each other in chains. Eight of those twenty, called essential amino acids, cannot be synthesized in the cells of humans and must be consumed as part of the diet. The remaining twelve are nonessential amino acids.

---

Etymology

Origin of amino acid

First recorded in 1895–1900

Compare meaning

How does amino-acid compare to similar and commonly confused words? Explore the most common comparisons:

• nucleic acid vs. amino acid

Example Sentences

To create the compounds, the researchers combined several amino acids with tryptamine, a naturally occurring metabolite derived from the essential amino acid tryptophan.

From Science Daily • May 14, 2026

That’s despite few clinical studies supporting the effectiveness or safety of these peptides, which are amino acid chains meant to help regulate functions in the body and have become popular among fitness and longevity enthusiasts.

From Salon • Apr. 4, 2026

They found that a mirror version of cysteine, a sulfur-containing amino acid, can significantly slow the growth of certain tumors while leaving healthy cells largely unaffected.

From Science Daily • Mar. 12, 2026

It also includes L-theanine, an amino acid that naturally occurs in green tea, which is also understood to have a relaxing effect on the body to aid sleep.

From BBC • Mar. 5, 2026

In order for the toxic compound to be excreted in the urine, it first has to bind with available molecules of glucose or amino acid.

From "Into the Wild" by Jon Krakauer