Editing Carotene (section)

==Molecular structure==
Carotenes are polyunsaturated [[hydrocarbon]]s containing 40 carbon atoms per molecule, variable numbers of hydrogen atoms, and no other elements. Some carotenes are terminated by rings, on one or both ends of the molecule. All are coloured, due to the presence of [[conjugated double bond]]s. Carotenes are [[tetraterpene]]s, meaning that they are derived from eight 5-carbon [[isoprene]] units (or four 10-carbon terpene units).

Carotenes are found in plants in two primary forms designated by characters from the [[Greek alphabet]]: [[alpha-Carotene|alpha-carotene]] (α-carotene) and [[beta-Carotene|beta-carotene]] (β-carotene). [[gamma-Carotene|Gamma-]], [[delta-Carotene|delta-]], [[epsilon-Carotene|epsilon-]], and [[zeta-Carotene|zeta-carotene]] (γ, δ, ε, and ζ-carotene) also exist. Since they are hydrocarbons, and therefore contain no oxygen, carotenes are fat-soluble and insoluble in water (in contrast with other [[carotenoid]]s, the [[xanthophyll]]s, which contain oxygen and thus are less chemically hydrophobic).