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Steroids are a family of lipid molecules that includes cholesterol, steroid hormones, and bile salts. These amphipathic molecules (containing both hydrophobic and hydrophilic regions) are derived from two-carbon acetyl-CoA units, whose combination leads to the formation of isoprenoids (five-carbon isoprene molecular units), and finally to the formation of a seventeen-carbon tetracyclic hydrocarbon, the steroid skeleton. Figure 1 shows the basic steroid skeleton structure, made up of three six-membered rings and one five-membered ring. The fused six-membered cyclohexane rings each have the chair conformation . Each member of the steroid family has a structure that differs from this basic skeleton in the degrees of unsaturation within the ring system and the identities of the hydrocarbon side chain substituents attached to the rings. These substituents are in most cases oxidized to alcohol, aldehyde , ketone , or carboxylic acid functional groups . The general term sterol refers to a subgroup of steroids that contain an alcohol functional group, which is signified by the -ol ending. Steroids are found predominantly in eukaryotic cells , with cholesterol being the most abundant steroid molecule. It contains twenty-seven carbons, has an alcohol functional group at C-3, a methyl group at C-13, and a branched aliphatic hydrocarbon (eight carbons) unit at the C-17 carbon atom. It is the basic building block for all the other steroid molecules. The biosynthesis of other steroids from cholesterol yields molecules that have fewer carbons, are more polar and more oxidized, and have smaller and more oxidized hydrocarbon units at C-17. It should be emphasized that cholesterol and most steroids contain predominantly single (Câ€“C) bonds and take on non-planar structures. Intracellular cholesterol is predominately found as part of (embedded in) the plasma cell membranes. Because of cholesterol's bulky structure, it does not embed well into the lipid bilayer structure of a membrane and as a result disrupts the order or regularity of the membrane. Increasing levels of embedded cholesterol, which can be as high as 25 percent of membrane volume, correlates with increasing the fluidity (as opposed to rigidity) of the membrane. The level of extracellular cholesterol in blood serum correlates with the degree of advancement of atherosclerosis and the development of coronary heart disease. The serum cholesterol is obtained from diet and from biosynthesis, which occurs primarily in the liver of mammals. The usual metabolic pathway for cholesterol biosynthesis involves a sequence of more than twenty reactions, each catalyzed by a specific enzyme. The committed and the rate-limiting step in the sequence is the synthesis of a six-carbon molecule, mevalonate, catalyzed by the enzyme 3-hydroxy-3-methylglutaryl CoA reductase (HMG CoA reductase). The development of drugs that inhibit the activity of HMG CoA reductase (and that reduce levels of serum cholesterol), has led to a decline in coronary heart disease. These drugs have structures similar to that of mevalonate and serve as competitive inhibitors of HMG CoA reductase. The binding of a competitive inhibitor to the enzyme and of the substrate mevalonate to the same enzyme are mutually exclusive events. One of the most potent inhibitors of HMG CoA reductase is the drug lovastatin, which binds very strongly at the active site of the enzyme, and, as a result, serum cholesterol levels in humans are decreased by as much as 20 percent. The hydrophobic, water-insoluble cholesterol is transported in blood to cells predominantly as part of high density and low density lipoprotein particles (HDLs and LDLs, respectively). LDLs transport cholesterol to extrahepatic tissues. The LDL particles bind to LDL receptors on the cell membranes, facilitating cholesterol deposition at the cells, for use primarily as a component of the membrane. HDLs carry out a similar transport function but also return cholesterol to the liver, where it can be metabolized. In this way HDLs decrease the levels of the cholesterol that contributes to the deposition of plaque in arteries and is implicated in heart disease. In a number of cases, patients have been found to have defective genes that code for the LDL receptors. In these cases the LDL particles cannot deposit the cholesterol at cell sites. The LDLs remain in the blood, and eventually their lipid molecules accumulate on the arterial walls, which can lead to blockage of arteries and a heart attack. Cholesterol is the precursor of other important steroid metabolites , which include bile salts and steroid hormones. Bile salts, which are the major breakdown product of cholesterol, resemble detergents, which are amphipathic molecules (having both polar and nonpolar regions). Their primary function is to emulsify dietary lipids. This interaction between bile salt and lipid increases the surface area of exposed lipid, which greatly enhances the ability of lipase enzymes to get access to and hydrolyze lipid molecules, thereby promoting their absorption and digestion. Bile salts are synthesized and secreted by the liver, stored in the gall bladder, and pass through the bile duct and into the small intestine. Bile salts are the major metabolic product of cholesterol, their manufacture accounting for the consumption of approximately 800 mg/day of cholesterol in a normal human adult. (On the other hand, less than one-tenth that amount of cholesterol is utilized for steroid hormone synthesis.) A major bile salt is glycocholate. Cholesterol is also the precursor of all the steroid hormones, which can be subdivided into five major classes. The first and second classes of hormones, the mineralocorticoids and the glucocorticoids , are synthesized in the adrenal cortex. The mineralocorticoids (e.g., aldosterone) regulate the body's ion balance by promoting the reabsorption of inorganic ions, such as Na+, Clâˆ’, and HCO3âˆ’, in the kidney. As a result, they are involved in the regulation of blood pressure. The glucocorticoids (e.g., cortisol) regulate gluconeogenesis and, in pharmacological doses, inhibit the inflammatory response. The third class includes progesterone , associated with the female reproductive cycle and synthesized in the cells of the corpus luteum; it prepares the lining of the uterus for implantation of the ovum and is essential for the maintenance of pregnancy. The sex hormones are synthesized in the male and female gonads and in the placenta. These hormones, the fourth and fifth classes, are androgens (primarily testosterone) and the estrogens (primarily estradiol). These two classes of hormones are associated with the development of the secondary sexual characteristics of males and females, respectively. They exert powerful physiological effects in humans because of their importance in the regulation of a variety of vital metabolic processes. Steroid hormones, like all hormones, are chemical messengers. They are synthesized in the cells of an endocrine gland, secreted by the cells into the bloodstream, and travel to target organs in which they direct cell-to-cell communication and the "global regulation" of metabolism in a multicellular organism such as humans. The levels of the steroid hormones are also highly regulated, with levels in the blood or in cells being very small, typically less than micromolar amounts. Because of their hydrophobic character, they must associate with carrier molecules for their transport in the blood. In contrast to polypeptide hormones that bind to hormone receptor proteins embedded in the plasma membranes of cells, the hydrophobic steroid hormones pass from the bloodstream into cells readily via passive diffusion across the membrane. Although the steroid hormones can in principle enter all cells, the only cells that are responsive to steroid hormones are those cells that contain proteins called steroid hormone receptors. These receptors reside in an inactive state either in the cytoplasm or in the cell nucleus. There are specific hormone receptors for each of the hormone types: estrogen , androgen, progesterone, glucocorticoid, and mineralcorticoid. As a result
steroids class of lipids having a particular molecular ring structure called the cyclopentanoperhydro-phenanthrene ring system. Steroids differ from one another in the structure of various side chains and additional rings. Steroids are common in both plants and animals. In humans, steroids are secreted by the ovaries and testes, the adrenal cortex (see adrenal gland ), and the placenta. The range of steroids is diverse, including several forms of vitamin D, digitalis, sterols (e.g., cholesterol ), and the bile acids. Many steroids are biologically active hormones that control a number of the body's metabolic processes. This group includes the male sex hormone testosterone and the female sex hormones estrogen and progesterone . The steroid hormones of the adrenal cortex include glucocorticoids such as cortisone and cortisol (see also corticosteroid drug ) and mineralocorticoids such as aldosterone . Natural or synthetic steroids are used in oral contraceptives and in the treatment of arthritis , Addison's disease , and certain skin ailments. Side effects, related to dosage and length of treatment, can be serious and include high blood pressure, edema, unwanted hair growth, and menstrual cycle disruption. Anabolic steroids , male hormones given to build up strength in seriously ill patients, have been abused by bodybuilders and athletes in an attempt to increase muscle mass and strength.
Anabolic steroids are synthetic chemicals that mimic the effects of the male sex hormone testosterone. Some athletes seeking increased muscular strength and size abuse anabolic steroids. They may reach their goal of increased strength in the short term but risk serious medical complications in the long term. "Anabolic" denotes the ability to induce protein synthesis, particularly in muscle cells. As a result, isometric muscle strength increases. These steroids are also androgenic, which means that they cause changes characteristic of males, such as growth of facial hair, loss of scalp hair, deepening of the voice, skin oiliness, and aggressive behavior. A female taking anabolic steroids experiences irregular menstrual periods and atrophy of the breasts and uterus, and develops the male-associated characteristics. A male may develop an enlarged prostate and atrophy of the testicles. Steroid abuse stunts height, increases weight, dampens immunity, and can damage the kidneys, liver, and heart. Blood vessels may become blocked with fatty plaque. The liver may develop tumors, and infertility is common. Psychiatric symptoms include depression, delusions, and violent tendencies, sometimes called "'roid rage." Athletes call anabolic steroids 'roids, juice, pump, or hype. Some of the one hundred varieties are oxymetholone, oxandrolone, and stanozolol (taken orally) and nandrolone and boldenone (taken by injection). Abusers may take one huge dose seeking instant strength, slowly build up the dose (pyramiding), or "stack" different types of steroids. Whatever the delivery route, the message to the body is the same: there's too much testosterone; halt normal production. Despite the well-known side effects of anabolic steroids, use among athletes is widespread, perhaps because of the example set by professional baseball, basketball, and hockey players who use them. However, the National Football League, International Olympic Committee, and National Collegiate Athletic Association ban their use. Still, about 30 percent of college and professional athletes use anabolic steroids, as do 10 to 20 percent of high school athletes. Among U.S. bodybuilders, studies show that steroid use exceeds 80 percent. Olympic athletes have often been punished for steroid use. After Canadian Ben Johnson flew past his competitors in the 100-meter run in the 1988 summer Olympics, officials rescinded his gold medal when a urine test revealed stanozolol in Johnson's system. His natural testosterone level was only 15 percent of a normal male's. Shot-putters, discus throwers, wrestlers, and swimmers have also been known to use anabolic steroids. In 2000, a urine test on U.S. shot-putter C. J. Hunter revealed one thousand times the allowable limit of nandrolone. Anabolic steroids do have legitimate medical uses. They were first synthesized in the 1930s to treat underdeveloped testes and resulting testosterone deficiency. In the 1950s, they were used to treat anemia and muscle-wasting disorders and to bulk up patients whose muscles had atrophied from extended bed rest. In the 1960s, anabolic steroids were used to treat some forms of dwarfism. Today anabolic steroids are being studied for their ability to alleviate the extreme body wasting associated with acquired immunodeficiency syndrome (AIDS). Their most common use, however, remains among athletes seeking a quick competitive edge. see also Endocrine System; Hormones; Male Reproductive System; Muscle Ricki Lewis American Academy of Pediatrics. Steroids: Play Safe, Play Fair.
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Answers:Basically because its so prevalent. As bad as it sounds, so many people do steroids that its really okay. The outcome of games aren't changed because there's steroid users on every single team, probably going back as far as 15 maybe 20 years. And both pitchers and hitters use steroids, so neither side really has much of an advantage. Where steroids does seem to make a difference is when guys like Barry Bonds and Roger Clemens get older, and they're even better than they were 10 years before. Enough players that aren't that good have been caught with steroids that its obvious you need to be incredibly talented to do the things that A-Rod and Bonds have done. I know that baseball is a game of numbers, but Barry Bonds having more career home runs than Hank Aaron doesn't take anything away from Aaron's legacy in my mind, and him having more single season home runs than Maris doesn't take anything away from Maris' in my mind. If you're so closed minded you really need to see Maris and Aaron at the top of the list and can't take into account the difference in eras then that's your problem. Do you really think Ty Cobb would have a .366 career average if he started playing today? I'm sure he'd be a great player, but even Ichiro wouldn't flirt with .366 for an entire career, and if he couldn't do it nobody could. The analogy between the deadball era and the steroid era isn't perfect, but if you're willing to accept the fact that around the early-mid 90s a legitimate steroid culture was born in MLB, then it's pretty close. Steroids isn't cheating because so many people do it. Look at the Mitchell report, there's tons of players of all qualities and longevities and teams, and we don't even know 5 of the 103 guys that actually tested positive. AND that's just the players that's there's evidence against, imagine how many have gotten away with it. I agree that it sort of sucks, but I love baseball too much to let something like steroids get in the way.
Answers:Steroids are lipids. Sterols are a type of steroid. Sterol is an alcohol version of a steroid with an OH (alcohol) group on the first (or alpha or A) 6-carbon ring. The steroid 4 ring system is made of up three 6-carbon rings and a 5-carbon ring.
Answers:Steroid hormones are lipophilic, which means they can cross the membrane of their target cells and therefore have an intracellular receptor. Steroid hormones work by inducing synthesis of proteins, therfore they influence the amount of enzymes inside the cell. Examples of steroid hormones include thyroid hormones and sex hormones. Protein hormones on the other hand are hydrophilic, and therefore cannot cross the membrane of their target cell. Consequently their receptor is located on the surface of the cell membrane. Protein hormones produce their desired response by causing activation or inactivation of target enzymes. Examples of protein hormones include insulin.
Answers:These are hormones synthesized from amino acids, whose actions are systemic, i.e. they don't have a specific target but act generally. Examples include; - creatine monohydrate which is popular as a food supplement, - human growth hormone, - insulin-like growth factor, and insulin. The examples above have been used (illegally) by athletes to enhance performance.