tetraterpenoid biosynthetic process carotenoid metabolic process carotenoid biosynthetic process carotenoid synthesis carotenoid formation MetaCyc:CAROTENOID-PWY GO:0016117 The chemical reactions and pathways resulting in the formation of carotenoids, tetraterpenoid compounds in which two units of 4 isoprenoid residues joined head-to-tail are themselves joined tail-to-tail. biological_process carotenoid biosynthesis carotenoid anabolism pigment biosynthetic process