The biosynthesis of steroids begins with acetyl coa being turned into acetoacetyl through a acetoacetyl CoA thiolase. Acetoacetyl -CoA reacts with an acetyl-CoA and water through a 3-hydroxy 3-methylglutaryl coenzyme A synthase resulting in the release of coenzyme A, hydrogen ion and (S)-3-hydroxy-3-methylglutaryl-CoA. The latter compound reacts with NADPH and a hydrogen ion through a 3-hydroxy-3-methylglutaryl-coenzyme A resulting in the release of coenzyme A , NADP and mevalonate. Mevalonate is then phosphorylated through an ATP driven kinase mevalonate kinase resulting in the release of ADP, hydrogen ion and mevalonate 5-phosphate. The latter compound is phosphorylated through an ATP driven kinase, phosphomevalonate kinase resulting in the release of ADP and mevalonate diphosphate. This latter compound then reacts with an ATP driven mevalonate diphosphate decarboxylase resulting in the release of ADP, carbon dioxide, a phosphate and a isopentenyl diphosphate. The latter compound can be isomerized into dimethylallyl diphosphate or reacth with a dimethylallyl diphosphate to produce geranyl diphosphate. Geranyl diphosphate reacts with a isopentenyl through a farnesyl diphosphate synthase resulting in the release of diphosphate and farnesyl diphosphate. The latter compound reacts with hydrogen ion, NADPH through a squalene synthetase resulting in the release NADP, pyrophosphate and squalene. The latter compound reacts with hydrogen ion NADPH and oxygen through squalene monooxygenase resulting in the release of NADP, Water and (3S)-2,3-epoxy-2,3-dihydrosqualene. The latter compound reacts through a 2,3-oxidosqualene lanosterol cyclase resulting in the release of lanosterol. Lanosterol reacts with hydrogen ion, NADPH, and oxygen through a cytochrome P450 lanosterol 14a demethylase resulting in the release of formate, water, NADP and 14-demethyllanosterol. The latter compound reacts with hydrogen ion and NADPH through a c-14 sterol reductase resulting in the release of NADP and 4,4-dimethylzymosterol. The latter compound reacts with methylsterol monooxygenase resulting in the release of 4α-hydroxymethyl-4β-methyl-5α-cholesta-8,24-dien-3β-ol which reacts with methylsterol monooxygenase twice to obtain 4α-carboxy-4β-methyl-5α-cholesta-8,24-dien-3β-ol. The latter compound then reacts with an NADP C-3 sterol dehydrogenase resulting in the release of water, NADP and 3-dehydro-4-methylzymosterol. The latter compound then reacts with NADPH and a hydrogen ion through a 3-keto sterol reductase resulting in the release of NADP and 4alpha-methyl-zymosterol. The latter compound then reacts with a methylsterol monooxygenase 3 times, followed by one reaction with c-sterol dehydrogenase and one reaction with 3-keto sterol reductase resulting in the release of a zymosterol. The latter compound reacts with SAM through a sterol methyltransferase resulting in the release of s-adenosylhomocysteine and fecosterol. Fecosterol is isomerized into episterol. The latter compound reacts with c-5 sterol desaturase resulting in the release of ergosta-5,7,24(28)-trien-3β-ol which then reacts with a c-22 sterol desaturase resulting in the release of ergosta-5,7,22,24(28)-tetraen-3-β-ol. This latter compound then reacts with a C-24 sterol reductase resulting in the release of an ergosterol.

Steroid Biosynthesis References