Ubiquinone (also known as Coenzyme Q or CoQ) biosynthesis occurs on the inner mitochondrial membrane and includes four main steps (i) the synthesis of the benzoquinone head ring from tyrosine; (ii) the synthesis of the isoprenoid chain tail; (iii) the condensation of head and tail; and (iv) the sequential modification of the benzoquinone head ring. The isoprenoid chain varies in length depending on the species. In D. melanogaster, there are 3 species of coenzyme Q ranging from 8 to 10 (CoQ8 to CoQ10) isoprenoid units with CoQ9 being the main species. CoQ exists in three oxidation states: fully reduced ubiquinol, the radical semiquinone intermediate and the fully oxidized ubiquinone form allowing it to act as an electron carrier. Its major roles are as an electron shuttle in oxidative phosphorylation and as an antioxidant. (Adapted from PMID:34198496, FBrf0260507 and FBrf0261808.)