| This contest is fueled by the following news: |
| | Judging and jury scandals in gymnastics and equestrian, as well as the doping issue - featuring prominently again on Wednesday - leading to 'wrong' medal ceremonies are not doing the Olympic image good.
Although the doping issue has been prominent throughout the Games, International Olympic Committee spokeswoman Giselle Davies warned not to blow the doping issue out of proportion.
Steroids - class of organic compounds, belonging to isoprenoids with respect to chemical nature. Various kinds of steroids are widely spread in wildlife and are also found in microorganisms, plants and animals; one of the basic directions of chemical evolution of steroids— their specialization as biological regulators — hormones etc.
Formally, all the steroids are derivatives of hypothetical hydrocarbon of sterane (I, R =H) and bio-genetically occur from squalene, which transforms into closest polycyclic predecessors of steroids— lanosterol (in animals) or cycloartenol (plants), containing 30 atoms of carbon (C30). Almost all the steroids are crystallic substances, possessing optic activity and better soluble in organic solvents than in water.
Classification of steroids is based on their chemical structure and nature of physiological effect or function, which allows to divide into following groups. 1) Sterols, containing branched side chain of R from 8—10 atoms of carbon. Sterols are part of animal and vegetative lipids; important steroid amongst sterols — cholesterol, which participates in biosynthesis of steroids and hormones. 2) D Vitamins: Unsaturated isomers of sterols (with open ring B) and participate in regulation of calcium metabolism and formation of skeleton in vertebrates.3) Bile alcohols and bile acids, containing hydroxyl or carboxyl group in side ring (of 8 or 5 carbon atoms); Help in food digestion in intestines in vertebrates.4) Aglycones (Genins) are steroid saponins and steroid glycoalkaloids. Diosgenin (II, Х=О) and solasodin (II, Х == NH) are typical representatives of aglycones; both groups are characteristic for plants of lily, figwort and solanaceous family and possess surface active and hemolytic properties in the form of glycosides. 5) Steroid alkaloids of other types: С27-alkaloids with modified steroid skeleton, stimulating reduction of cross-striated muscles; vegetative С21-alkaloids, possessing bactericidal and amebicidal effects and modified С21-alkaloids from glands of amphibians (samandaron, batrachotoxin, etc.), being strong poisons of central nervous system and cardio toxins. 6) Cardiac genins, containing side ring in the form of unsaturated pentamerous (С23-cardenolides) or hexamerous (C24-bufadienolides) lactone cycle; possess ability to bolster the reduction of cardiac muscle by inhibiting the enzyme LTF-elements in membranes of heart cells; cardenolides are found in many plants, bufadienolides — predominantly in poison from skin glands of toads. 7) Steroidal sexual hormones and their transformation products, defining the development and functioning of sexual system in animals. Progesterone and its related C-21 compounds, in which the side ring R contains two carbon atoms and also male sexual hormones — androgens, containing 19 carbon atoms and female sexual hormones —oestrogens, containing 18 carbon atoms; hydroxyl or carbonyl group is found inside ring for androgens & oestrogens. All these belong to steroidal sexual hormones. 8) Hormones of cortex of adrenal glands — corticosteroids (R = СОСН2ОН); regulate the balance of electrolytes and carbohydrate metabolism in organism of vertebrates. They are close to steroids, some oxylisine antibiotics fusidic acid, cephalosporin P1) & other oxylisines.
Biosynthesis ability of steroids is most brightly expressed in higher vertebrates. Insects do not produce steroids and receive them through food, however, molting function, which is vital for the insects, is controlled by special variety of С27-sterols — ecdysones, derivatives of progesterone serve for a number of insect types as means of chemical protection. In some lower-order mushrooms (Achlya, etc.), sexual reproduction is also induced by steroids. It can be possible that steroids take part in morphogenesis in vascular plants. Inhibitors of biosynthesis of steroids disturb reproduction of some mushrooms and flowering in higher-order plants.
Chemistry, biochemistry and physiological activity of steroids are intensively studied due to great value of steroids in medicine, veterinary science and animal husbandry. Chemical and microbiological methods of partial synthesis of steroid hormones from accessible natural raw materials (sterols, bile acids, saponins) and in 60-70s of 20th century — also methods of their full chemical synthesis from elementary initial substances are mastered in industry. Synthesis of “artificial” steroid hormones with specialized physiological action (contraceptive, anabolic, etc.), in particular, fluorine-containing and nitrogen-containing analogues, acquire huge importance. |
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