Steroid biological roles

Terpenes (and terpenoids) are further classified according to the number of 5-carbon units they contain. Thus, monoterpenes are 10-carbon substances biosynthesized from two isoprene units, sesquiterpenes are 15-carbon molecules from three isoprene units, diterpenes are 20-carbon substances from four isoprene units, and so on. Monoterpenes and sesquiterpenes are found primarily in plants, but the higher terpenoids occur in both plants and animals, and many have important biological roles. The triterpenoid lanosterol, for example, is the precursor from which all steroid hormones are made. 

All of these biological roles of the steroids figure prominently in human well-being. Defects in cholesterol metabolism are major causes of cardiovascular disease. It is no wonder that steroids are a central concern in medical biochemistry. In this chapter we discuss the metabolism of these complex lipids and the plasma lipoproteins in which they and other complex lipids are transported to various tissues. 

Terpenes are are a class of compounds whose chemical structures are based on a number of isoprene units , derived from the hydrocarbon CH2=C(CH3)-CH=CH2 they may themselves be hydrocarbons, but may also contain alcohol (OH), aldehyde/ketone (CO) and carboxylic acid (COOH) groups. Monoterpenes are Cm compounds derived from two isoprene units, sesquiterpenes (Cu) are derived from three isoprene units, diterpenes (C20) from four and tritepenes (C30) from six. Terpenes are widespread in plants, where they are largely responsible for the odor, and they are the major constituents of plant-derived essential oUs . Among the best known terpenes are 3-pinene (turpentine), camphor, menthol and citroneUal (aU monoterpenes) and farnesol (a sesquiterpene that is a constituent of the essential oils of many plants). Certain terpenes have important biological roles vitamin A, for example, is a diterpene, and steroid hormones have a structure related to triterpenes (and are biosynthesized by a similar route). 

Pike, J.W. (1987) Emerging concepts on the biologic role and mechanism of action of 1,25-dihydroxyvitamin D3. Steroids, 49, 3-27. 

Triterpenes (six isoprene units) and tetraterpenes (eight isoprene units) have important biological roles. For example, squalene, a triterpene, is a precursor of steroid molecules (Section 26.9). 

Steroids constitute an important class of naturally occurring compounds that fill many important biological roles Cholesterol is a steroid, and sex hormones are steroids. People were—and still are— interested in the synthesis of steroids for medical use (the introduction of the culture-altering birth control pill hinged on a steroid synthesis). At this time however they were being confounded by some unexplained chemical behavior of steroids. During Fieser s lecture Barton, aware of Hassel s work because of his reading habits, realized he could explain the anomalous reactivity of steroids. 

Other steroids are common in animal tissues and play important biological roles. Cholic acid, for example, occurs in the bile duct, where it is present mainly in the form of various amide salts. These salts have a polar region (hydrophilic) and a largely hydrocarbon region (lipophilic) and function as emulsifying agents to facilitate the absorption of fats in the intestinal tract. They are, in a sense, biological soaps. 

The same fused, four-ring core structure is present in the steroids, which have different biological roles as hormones and signaling molecules. The C18 steroids include the estrogen family, whereas the C19 steroids constitute the androgens, such as testosterone and androsterone. The C21 subclass includes the progestogens, the glucocorticoids, and mineralocorticoids. 

Steroids are a class of lipids characterized by a sterane core and additional functional groups. Hundreds of distinct steroids are found in plants, animals, and fungi. It is possible to classify steroids based on their chemical composition into cholestanes (e.g., cholesterol), cholanes (e.g., cholic acid), pregnanes (e.g., progesterone), and androstanes (e.g., testosterone and androgen). Steroids play many important biological roles, often as hormones interacting with specific receptors. The hydrophobic... 

It is interesting to note that 20a-dihydroprogesterone can have a biological role in humans. It has been established that this steroid controls the 3 8-hydroxydohydrogenase, Aj —> A4 isomerase activity and consequently inhibits the conversion of pregnenolone to progesterone. At the same time, the placental estrogens control the 20a-reductase activity (Wiener and... 

It has been well established that in adults some steroid ester sulfates act in the biosynthesis and in the intermediate metabolism of stciroid hormones and that steroid glucuronides are genera% the final step in the transformation of steroids. However, as a result of recent work carried out during fetal life in human.s as well as in animals, the possibility is now recognized that steroid ester sulfates play an important biological role in the... 

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