Hey it’s professor dave, i’m going to tell you about steroids. When people hear the word steroids, they typically think of anabolic steroids, which are synthetic derivatives of testosterone, but in actuality, steroids refer to a class of molecules that includes not just hormones, but also certain vitamins and cholesterol. Let’s learn a bit about the structure and function of steroids. Steroids are all derivatives of this.
Ring system, which is comprised of four rings. the a, b, and c rings are six membered rings while the D ring is a fivemembered ring. There are also always methyl groups on these two carbons, and for ease of communication we will always number this ring system the following way: This is carbon 1, and numbers 110 will wrap around rings A and B this way. Then carbon 11 jumps over to ring C and we wrap around rings C and D, lastly.
Numbering these two methyl groups like this. all the steroids we examine will be based on this structure. Now we know that sixmembered rings like to be in chair conformations, so let’s see what that would actually look like. First we should note that there are two common conformations for the A ring either with a trans ring junction between A and B like this, or a cis junction putting ring A like this.
Also notice that the methyls are in the axial position pointing upwards, and we will commonly refer to the substituents on the same side as those methyls as beta substituents, whereas ones on the other side, trans to the methyls, will be alpha substituents. The orientation of a ring will depend on the hydrogen on carbon 5. If that hydrogen is alpha, or on the dash bond you get the trans AB junction. If the hydrogen is beta, or on the wedge bond, you get the cis AB junction.
Now, where else do steroids vary in structure? a common location for a substituent is carbon 17. Different alkyl groups at this location will generate different steroids, one of which is cholesterol. Cholesterol has eight stereocenters which means 256 different stereoisomers of this structure are possible, but only this specific one is cholesterol. This is an intermediate in the biosynthesis of all the steroids we need.
In our body, and although we often consume cholesterol, we don’t need to because we also make it ourselves, so we will typically have more cholesterol than we need, and too much cholesterol in the diet leads to clogged arteries and heart problems. Let’s look at another type of steroid, the sex hormones. These can be divided into three classes: the female hormones or estrogens, the male hormones or.
Androgens, and pregnancy hormones or progestin. let’s look at the female hormones first. These are estrone and estradiol,l which differ only in the level of oxidation at carbon 17. Estradiol is secreted by the ovaries and kicks off the changes that occur during puberty, and also causes development of the mammary glands during pregnancy, whereas estrone is just a metabolized form of estradiol that is excreted.
The male sex hormones, and androsterone and testosterone, are incredibly similar to the female hormones, with the only differences occurring in the A ring. Similarly to the female hormones, testosterone does all the work, promoting the growth of body hair and facial hair, lowering of the voice and other traits associated with puberty, whereas androsterone is just the metabolized version that is excreted into the urine. And progesterone is the most important.