Glycine (Gly, G)
Nonpolar, aliphatic side chain, conditionally essential in the human diet
What is the charge of glycine at pH 7.4?
At pH 7.4, the pH of blood plasma, glycine carries a net charge of −0.01, and 99% of its molecules are the zwitterion, charge 0. Its side chain does not ionize, so only the α-carboxyl and α-amino groups are charged, and their charges nearly cancel. Its isoelectric point is 5.97, from Lehninger’s pKa values of 2.34 and 9.60.
Properties of glycine
| Three-letter code | Gly |
|---|---|
| One-letter code | G |
| Side-chain class (Lehninger) | Nonpolar, aliphatic |
| Side-chain group | one hydrogen |
| Formula (uncharged form) | C₂H₅NO₂ |
| Molar mass | 75.07 g/mol |
| pK₁ (α-carboxyl) | 2.34 |
| pK₂ (α-amino) | 9.60 |
| pKR (side chain) | none, the side chain does not ionize |
| Isoelectric point (pI) | 5.97 |
| Configuration at Cα (L form) | none, not chiral |
| Hydropathy (Kyte and Doolittle) | −0.4 |
| mRNA codons | GGU, GGC, GGA, GGG |
| Human diet | Conditionally essential |
pKa values and pI from Nelson and Cox, Lehninger Principles of Biochemistry, 7th edition, Table 3-1. Formula and molar mass from the wwPDB Chemical Component Dictionary and the IUPAC standard atomic weights; codons from NCBI translation table 1; hydropathy from Kyte and Doolittle (1982); diet from the Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005), chapter 10.
The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.
Charge of glycine at common pH values
| pH | Net charge | Most common form | Share of molecules |
|---|---|---|---|
| 1 | +0.96 | cation (+1) | 96% |
| 3 | +0.18 | zwitterion (0) | 82% |
| 5 | 0.00 | zwitterion (0) | 99.8% |
| 7 | 0.00 | zwitterion (0) | 99.7% |
| 7.4 (blood plasma) | −0.01 | zwitterion (0) | 99% |
| 9 | −0.20 | zwitterion (0) | 80% |
| 11 | −0.96 | anion (−1) | 96% |
| 13 | −1.00 | anion (−1) | over 99.9% |
The net charge is an average over all the molecules, so it can be a fraction; each molecule carries a whole number of charges, and the most common form is the one protonation state with the largest share.
Which form dominates between the pKas
- Below pH 2.34: the cation, net charge +1.
- pH 2.34 to 9.60: the zwitterion, net charge 0.
- Above pH 9.60: the anion, net charge −1.
Open glycine in the Amino Acid 3D Explorer and drag the pH to watch each group gain and lose its proton, with every pKa and its pI marked on the pH slider.
How the charge at pH 7.4 is calculated
Each group is treated on its own with the Henderson-Hasselbalch equation. An acidic group adds
−1/(1 + 10^(pKa − pH)), the share of molecules in which it has lost its proton, and a basic group
adds +1/(1 + 10^(pH − pKa)), the share in which it holds one.
Net charge of glycine at pH 7.4
- α-carboxyl (pK₁ = 2.34): −1/(1 + 10^(2.34 − 7.4)) = −1.0000
- α-amino (pK₂ = 9.60): +1/(1 + 10^(7.4 − 9.60)) = +0.9937
- q = −1.0000 + 0.9937 = −0.0063
- q ≈ −0.01
How to calculate the pI of glycine
Glycine has two ionizable groups, so its neutral form, the zwitterion, lies between them and the pI is the mean of pK₁ and pK₂.
Isoelectric point of glycine
- pI = (pK₁ + pK₂)/2
- = (2.34 + 9.60)/2
- = 5.97
Stereochemistry
Glycine is the only one of the 20 that is not chiral. Its side chain is a second hydrogen, so its α-carbon carries two identical groups and it has no L or D form. The R and S Configuration Explorer ranks the groups on a stereocenter step by step.
How glycine compares with the other 19
- Glycine is one of 7 amino acids in the class Lehninger calls nonpolar, aliphatic; the others are alanine, proline, valine, leucine, isoleucine and methionine.
- Its molar mass, 75.07 g/mol, makes it the lightest of the 20.
- Its pI, 5.97, is the joint 8th highest of the 20, with valine.
- On Kyte and Doolittle’s hydropathy scale it scores −0.4, the 8th most hydrophobic of the 20.
- It has 4 codons, as do 4 of the other 19.
Is glycine an essential amino acid?
Only conditionally. Glycine is one of 6 conditionally essential amino acids: the body makes it, but needs it from food when its own synthesis cannot keep up with demand. The other 5 are arginine, cysteine, glutamine, proline and tyrosine.
Classification from the Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005), chapter 10, which calls the three lists indispensable, conditionally indispensable and dispensable.
Codons for glycine
Glycine is encoded by 4 of the 61 sense codons in the standard genetic code: GGU, GGC, GGA and GGG in mRNA, written GGT, GGC, GGA and GGG on the DNA coding strand.
The DNA to Protein Translator reads codons in a sequence of your own, and the Protein Synthesis Simulator builds the chain on a ribosome, one amino acid per codon.
Work with glycine
- Amino Acid 3D Explorer: glycine in 3D, with its charge at any pH
- Molar mass of C₂H₅NO₂, worked out atom by atom in the Molar Mass Calculator
- Henderson-Hasselbalch Calculator: the acid to base ratio of one group at any pH
- Titration Curve Calculator: the curve for a weak acid titrated with a strong base
- All 20 amino acids: pKa values, pI, charge and codons in one table
- Glycine on Wikipedia