Glycine

Ball-and-stick Stick Space-filling

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10 atoms, 9 bonds.

IUPAC name: 2-aminoacetic acid
Molar mass: 75.0670(80) g/mol
Atoms: 10
SMILES: C(C(=O)O)N
InChIKey: DHMQDGOQFOQNFH-UHFFFAOYSA-N
PubChem CID: 750

Made of

Structural formula of glycine. Each unlabelled corner is a carbon atom, and the two hydrogens on carbon are not drawn. It shows which atoms are joined to which, not the shape. The model above shows the shape.

Where other amino acids carry a side chain of several atoms, glycine has a single hydrogen. ChEBI, the Chemical Entities of Biological Interest database, calls it the simplest amino acid that cells build into proteins, and the only achiral one. That means its mirror image is the same molecule rather than a distinct form. Its IUPAC name, 2-aminoacetic acid, describes an acetic acid whose second carbon holds an amino group, –NH₂. Two carbon atoms, one nitrogen, two oxygen and five hydrogen atoms add up to 75.07 g/mol.

The pure substance forms sweet-tasting white crystals. The Hazardous Substances Data Bank (HSDB) lists it as very soluble in water but insoluble in ethanol and ether, and records three crystal forms, alpha, beta and gamma. Heating gives no clean melting point: the crystals brown at 228 °C and begin to decompose at 233 °C, on HSDB’s figures.

Structure and bonding

Glycine’s ten atoms are one nitrogen, two carbons, two oxygens and five hydrogens. Both O atoms sit on the same carbon at one end of the chain. In the Ball-and-stick view the middle carbon, the CH₂ group, holds four single bonds, to nitrogen, to the carboxyl carbon and to two hydrogens. Chem1 describes such bonds pointing towards the corners of a tetrahedron, as in methane.

The carboxyl carbon beyond it carries one oxygen by a double bond, drawn as two sticks, and a second oxygen bearing the only O–H hydrogen. The Stick view leaves only the bonds, and the Space-filling view merges the ten atoms into one compact outline.

The drawing is the uncharged molecule, H₂N–CH₂–COOH, with no formal charges. ChEBI lists glycine as a tautomer of a glycine zwitterion, which carries a positive and a negative charge within one molecule. A tautomer is an isomer that differs only in where a hydrogen sits. It also names two ions: glycinium, formed when glycine gains a proton, and glycinate, formed when it loses one.

Where it turns up

MeSH, the US National Library of Medicine’s subject vocabulary, places glycine mainly in gelatin and in the silk protein fibroin. HSDB lists both, with sugar cane, as materials it has been isolated from. It has also been reported in plants such as Pinus densiflora and Cyperus aromaticus. Industry makes it from chloroacetic acid and ammonia, according to HSDB. US production reported to the Environmental Protection Agency (EPA) sat between 10 million and 25 million pounds a year from 2020 to 2023.

Food-grade glycine is an odourless white crystalline powder. The US Food and Drug Administration (FDA) lists it as a flavouring agent and nutritional supplement. HSDB adds that it reduces the bitter taste of saccharin and slows fats from going rancid. Cosmetics use it as a buffer, an antistatic agent and a hair and skin conditioner, and it appears in 53 personal-care products in the Consumer Product Information Database.

Why it matters

In the nervous system glycine sends two opposite kinds of signal. MeSH calls it a fast inhibitory neurotransmitter, a chemical messenger that damps activity in the nerve cell receiving it. At ionotropic receptors, which are ion channels, it triggers an influx of chloride ions, which creates an inhibitory potential, according to the US National Cancer Institute’s thesaurus. At NMDA (N-methyl-D-aspartate) receptors it instead joins glutamate as a co-agonist, helping along an excitatory potential, a push to fire.

HSDB records that glycine hyperpolarises motor nerve cells, making their inside more negative, with chloride passing more easily. Strychnine selectively blocks those effects, the main evidence, on HSDB’s account, that glycine mediates inhibition inside the spinal cord. Animals also use it to dispose of aromatic carboxylic acids, joining them to glycine as peptide conjugates.

Medicine puts it into intravenous feeding, into antacids as a buffer and into the irrigating fluid for transurethral removal of the prostate. MeSH lists it as non-essential, one the body can make. Young birds and poultry are an exception: HSDB reports that they need it in their feed.

Properties

Properties of glycine Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 750.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₂H₅NO₂
Molar mass	75.0670(80) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	2
Hydrogen atoms	5
Nitrogen atoms	1
Oxygen atoms	2
Bonds	9
Single bonds	8
Double bonds	1
PubChem molecular weight	75.07 g/mol	g/mol	PubChem

Safety

Glycine in food, supplements and cosmetics is essentially harmless. The EPA’s Safer Choice programme lists it as of verified low concern, and it meets no Globally Harmonized System hazard criteria in 96.7% of 602 company reports. Its reference sheet is the PubChem Laboratory Chemical Safety Summary.

Questions

Why is glycine the simplest amino acid?

Its side chain is a single hydrogen atom. Chem1 writes the amino acids that proteins are made from as R–CH(NH₂)COOH, and ChEBI gives glycine a hydrogen atom as its side chain, so in glycine R is simply H. That leaves the middle carbon with two hydrogens. Proteins are built from 20 different amino acids, the National Human Genome Research Institute notes.

What does the 3D model of glycine show?

Ten atoms and nine bonds: an amino group, a CH₂ carbon and a carboxyl group in a short chain. The carboxyl carbon carries one double-bonded oxygen and one O–H. It draws the neutral form, with an –NH₂ group at one end and –COOH at the other. ChEBI also records a zwitterion form, which carries a positive and a negative charge in the same molecule, and two ions, glycinium (one proton more) and glycinate (one proton fewer).

Is glycine an acid or a base?

It is both. CAMEO Chemicals, a hazard database, says glycine has the characteristics of an acid and of a base, and a 0.2 molar solution in water has a pH of 4.0, so it acts as a weak acid. HSDB gives two dissociation constants, pK 2.34 and 9.60, numbers that measure how readily the molecule gives up a proton, and puts the isoelectric point, the pH at which it carries no overall charge, at 5.97.

How is glycine obtained from gelatin and silk?

Glycine has been isolated from the products of hydrolysis, a reaction that splits a substance using water, of gelatin, cattle ligaments and silk. Kingston and Schryver published its isolation from gelatin hydrolysis products in the Biochemical Journal in 1924. A 1938 US patent assigned to Armour and Company used hydrolysed cattle ligaments, and Moore and Stein reported isolating it from silk fibroin in 1943.

Made of the same elements

C₃H₇NO₂ Alanine 13 atoms, 12 bonds.
C₄H₄N₂O₂ Uracil 12 atoms, 12 bonds.
CO(NH₂)₂ Urea 8 atoms, 7 bonds.
C₄H₅N₃O Cytosine 13 atoms, 13 bonds.
C₅H₆N₂O₂ Thymine 15 atoms, 15 bonds.
C₅H₅N₅O Guanine 16 atoms, 17 bonds.
C₅H₄N₄O₃ Uric acid 16 atoms, 17 bonds.
C₅H₉NO₄ Glutamic acid 19 atoms, 18 bonds.

All 25 compounds made of carbon, hydrogen, nitrogen and oxygen

C₈H₉NO₂ Acetaminophen 20 atoms, 20 bonds.
C₈H₁₁NO₂ Dopamine 22 atoms, 22 bonds.
C₆H₁₃NO₂ Isoleucine 22 atoms, 21 bonds.
C₆H₁₃NO₂ Leucine 22 atoms, 21 bonds.
C₉H₁₁NO₂ Phenylalanine 23 atoms, 23 bonds.
C₈H₁₀N₄O₂ Caffeine 24 atoms, 25 bonds.
C₉H₁₁NO₃ Tyrosine 24 atoms, 24 bonds.
C₉H₁₃NO₃ Epinephrine 26 atoms, 26 bonds.
C₁₀H₁₂N₂O Serotonin 25 atoms, 26 bonds.
C₁₁H₁₂N₂O₂ Tryptophan 27 atoms, 28 bonds.
C₁₂H₁₇NO DEET 31 atoms, 31 bonds.
C₁₃H₁₆N₂O₂ Melatonin 33 atoms, 34 bonds.
C₁₃H₂₁NO₃ Albuterol 38 atoms, 38 bonds.
C₁₄H₁₈N₂O₅ Aspartame 39 atoms, 39 bonds.
C₁₄H₂₂N₂O Lidocaine 39 atoms, 39 bonds.
C₁₇H₂₁NO Diphenhydramine 40 atoms, 41 bonds.
C₂₀H₂₄N₂O₂ Quinine 48 atoms, 51 bonds.