Lipids Part 2: Steroids

Steroids are a class of molecules that include hormones, vitamins, and cholesterol, beyond just anabolic steroids. They all share a distinct four-ring structure (A, B, C, D) with specific numbering conventions and always contain methyl groups on two carbons.

Six-membered rings in steroids adopt chair conformations. The A ring can have a trans or cis ring junction with the B ring, depending on the orientation of hydrogen on carbon 5. Substituents on the same side as the methyl groups are called beta, while those on the opposite side are alpha.

Steroids vary in structure at carbon 17. Cholesterol, an example, has eight stereocenters, but only one specific stereoisomer is cholesterol. It's an intermediate in the biosynthesis of all bodily steroids. While we consume it, our bodies also produce it, and excessive cholesterol can lead to health issues like clogged arteries.

Sex hormones are divided into estrogens (female), androgens (male), and progestins (pregnancy). Estrone and estradiol are female hormones, with estradiol initiating puberty and mammary gland development during pregnancy, while estrone is a metabolized form. Male hormones, androsterone and testosterone, are similar; testosterone promotes male secondary sexual characteristics, with androsterone being a metabolized version. Progesterone is crucial for preparing the uterus for implantation and suppressing ovulation during pregnancy.

Other steroid hormones like cortisol regulate various biological activities, including metabolism and inflammation.