From The School of Biomedical Sciences Wiki
Jump to: navigation, search

Testosterone (systematic name being 17beta-Hydroxyandrost-4-en-3-one) is a steroid sex hormone. It is a nongaseous signal molecule that is both hydrophobic and small[1].

In males, it is produced in the testicles and promotes male secondary sexual characteristics such as increased muscle growth, a deeper voice, production of sperm and development of sexual characteristics[2].

Like other steroid hormones, the precursor to these chemicals is cholesterol. More specifically, testosterone is an androgen hormone, one of the five major classes of steroid hormones, which also includes: progestagens, glucocorticoids, mineralocorticoids and estrogens[3]. Conversion of cholesterol to testosterone follows a number of steps and intermediate products: The starting reaction for any steroid hormone is the interaction between cholesterol and the cholesterol-side-chain-cleavage enzyme (P450scc). This results in the production of pregnenolone. From here, this is where differentiation of the hormones occurs. For the production of testosterone, pregnenolone interacts with the P450c17 enzyme and produces 17alpha-Hydroxy-pregnenolone. Further interaction with P450c17 results in dehydroepiandrosterone (DHEA). From here, DHEA can either: react with 3beta-HSD2 enzyme and produce androst-4-ene 3,17-dione or react with 17beta-HSD3 enzyme and produce androst-5-ene 3beta, 17beta-diol. Finally, from here the androst-4-ene 3,17-dione can react with 17beta-HSD3 enzyme and produce testosterone. On the other hand, androst-5-ene 3beta, 17beta-diol reacts with the 3beta-HSD2 enzyme and result in testosterone, which has an end number of 19C[4].


  1. Alberts, Johnson, Lewis, Raff, Roberts and Walter. (2008) 'Molecular Biology of the Cell' 5th Edition. New York: Garlands Science. p 889
  2. The Reproductive System at a Glance By Linda J. Heffner, Danny J. Schust P.17
  3. Berg, J.M, Tymoczko, J.L, Gatto, G.J.Jr, Stryer, L. Biochemistry Eighth Edition. 2015
  4. Norman, A.W, Henry, H.L. Hormones Third Edition. 2015 p.47
Personal tools