Chemistry and Structure of Anabolic and Androgenic Steroids
By Zack - MuscleTalk Pro-member
Part 1: General Structure and Synthesis of Steroids:
Steroids have a variety of uses in the human body, including, but not limited to: controlling meiosis, carbohydrate metabolism, fat storage, muscle growth, immune function and nerve cell membrane chemistry. Steroids can be separated into three main groups: gonadal compounds, glucocorticoids and mineralcorticoids. This distinction depends on the site of synthesis of the steroid. The gonadal variety are mainly synthesized in the gonads, as is suggested by the name, while the glucocorticoids (eg cortisol, cortisone) and mineralcorticoids (eg aldosterone) are synthesized in the adrenal cortex.
Steroids can also be divided into groups by function: androgens, estrogens, progestogens, anabolics, and catabolics. The two main types of steroids that we will consider are anabolics and androgens. Androgens exert some kind of masculinizing physical effect on the body, while anabolics promote growth. However, these distinctions are not completely exclusive. For example, testosterone is synthesized by the adrenal cortex as well as the testes, and has both anabolic and androgenic properties.
Steroids are fat-soluble hormones with a tetracyclic base structure. The base structure consists of four fused rings: three cyclohexane rings and one cyclopentane. The basic structural backbone can be seen below:
As you can see, each of the rings is designated by a letter. Rings A and D are the most commonly modified rings. The following diagram shows the numbering of the carbons in steroids, which will be useful later in this article. The two methyl groups on C10 and C13 are also designated with numbers, as they are present in most steroids.
Steroids are synthesized in the body from squalene, a complex linear aromatic molecule shown below:
Squalene is cyclized to form cholesterol. In the first few steps of this chemical pathway, squalene is converted to squalene epoxide, which has a different double-bond bond distribution that is necessary for the ring fusion to occur. In ten complex steps of cyclization and carbocation, squalene epoxide is converted to Lanosterol. This reaction is catalyzed by the enzyme cyclase. The lanosterol is then downgraded, with three methyl groups being removed, and cholesterol is formed. This process of the cyclization of squalene is considered to be one of the most fascinating and complex reactions in organic chemistry.
Steroids are all cholesterol derivatives. Cholesterol is hydroxylated and modified by the enzyme cytochrome P-450 (removing the 6-carbon side chain at position C21) into Pregnenolone. This is a hormone secreted in the uterus controlling ovum implantation, and is the precursor for the androgens, estrogens, and glucocorticoids.
At the cellular and molecular level, all of the steroids function in a very similar way. Because they are fat-soluble, they can easily diffuse across the cell membrane into the cytoplasm. Once in the cytoplasm, the steroids bind to receptors, which are composed of proteins. This forms what is known as a steroid-receptor complex. The complexes then undergo dimerization, where two complexes bind together to form a dimer. The dimer will then travel to the nucleus of the cell and bind to DNA, where it promotes gene transcription and translation, leading to the production of proteins (protein synthesis).
This process is shown in the diagram below. The effects of a steroid on gene expression and protein production are very complicated and difficult to understand. Often, the protein that is produced as a result of the dimer binding to the DNA is a regulatory protein, which is responsible for activating or suppressing other genes. This causes somewhat of a chain reaction. Also, the effect a steroid has on genes is determined by the type of cell in which it is present. For these reasons, the actual effects of steroids on gene expression will not be examined in this article.
Part 2 - Structure of Specific Steroids and Reactions They Undergo
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