CHNOPS and CHON are mnemonic acronyms for the most common elements in living organisms. "CHON" stands for carbon, hydrogen, oxygen, and nitrogen, which together make up more than 95 percent of the mass of biological systems. "CHNOPS" adds phosphorus and sulfur.
Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur are the six most important chemical elements whose covalent combinations make up most biological molecules on Earth.[1] All of these elements are nonmetals.
| Element | Mass in plants | Mass in animals | Biological uses | |
|---|---|---|---|---|
| Carbon | 12% | 19% | Found in carbohydrates, lipids, nucleic acids, and proteins. | |
| Hydrogen | 10% | 10% | Found in water, carbohydrates, lipids, nucleic acids, and proteins. | |
| Nitrogen | 1% | 4% | Found in nucleic acids, proteins, some lipids (e.g. sphingolipids) and some polysaccharides (e.g. chitin) | |
| Oxygen | 77% | 63% | Found in water, carbohydrates, lipids, nucleic acids, and proteins. | |
| Phosphorus | <1% | <1% | Found in lipids, nucleic acids and proteins. | |
| Sulfur | <1% | <1% | Found in proteins and some polysaccharides. |
Sulfur is contained in the amino acids cysteine and methionine.[3] Phosphorus is contained in phospholipids, a class of lipids that are a major component of all cell membranes, as they can form lipid bilayers, which keep ions, proteins, and other molecules where they are needed for cell function, and prevent them from diffusing into areas where they should not be. Phosphate groups are also an essential component of the backbone of nucleic acids (general name for DNA & RNA) and are required to form ATP – the main molecule used as energy powering the cell in all living creatures.[4]
Carbonaceous asteroids are rich in CHON elements.[5] These asteroids are the most common type, and frequently collide with Earth as meteorites. Such collisions were especially common early in Earth's history, and these impactors may have been crucial in the formation of the planet's oceans.
The simplest compounds to contain all of the CHON elements are isomers fulminic acid (HCNO), isofulminic acid (HONC), cyanic acid (HOCN) and isocyanic acid (HNCO), having one of each atom.[6]