STEROIDShandouts - STEROIDS, BILE ACIDS, STEROID HORMONES...

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STEROIDS, BILE ACIDS, STEROID HORMONES Vitamins D
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Steroids form an important group of compounds based on the fundamental saturated tetracyclic hydrocarbon : cyclo- pentanoperhydrophenanthrene (sterane). The prefix „perhydro ” refers to the fact that all the necessary hydrogen atoms have been added to the compound to make it fully saturated
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Steroid nucleus Steroid nucleus consists of three cyclohexane rings and one cyclopentane ring fused together. The four rings in steroid nucleus are designated A, B, C, and D .
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Steroids are three-dimen- sional . Thus, the constituent carbon atoms and the hydrogen atoms of their substituents lie in different planes, giving rise to isomers
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Conformation There are four rings in a steroid skeleton and hence there are three fusion points. A/B, B/C and C/D rings share two carbons each (fusion).
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Natural steroids have two methyl groups Two methyl groups attached to C-10 and C-13 lie above the plane of the molecule and are customarily the points of reference for the describing the spatial orientation of other substituents in the steroid nucleus.
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For two-ring system, the structures of cis - and trans -fused rings look like this: When there are directed on the same side, it is called cis . When the tow hydrogens are oriented opposite to each other with the ring system thought to as forming a plane, the ring fusion is called trans.
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Cholesterol is one of the most important and abundant steroids in the body
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Cholesterol Composed of the steroid nucleus with methyl CH 3 – groups, an alkyl chain, and a hydroxyl group –OH attached CH 3 HO CH 3 CH 3 CH 3 CH 3
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Slightly less than half of the cholesterol in the body derives from biosynthesis de novo . Biosynthesis in the liver accounts for approximately 10%, and in the intestines approximately 15%, of the amount produced each day. Cholesterol synthesis occurs in the cytoplasm and microsomes from the two-carbon acetate group of acetyl-CoA .
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Biosynthesis of Cholesterol The process has five major steps : 1. Acetyl-CoAs are converted to 3-hydroxy-3-methylglutaryl- CoA (HMG-CoA) 2. HMG-CoA is converted to mevalonate 3. Mevalonate is converted to the isoprene based molecule, isopentenyl pyrophosphate (IPP ), with the concomitant loss of CO 2 4. IPP is converted to squalene 5. Squalene is converted to cholesterol.
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Cholesterol is an extremely important biological molecule that has roles in membrane structure as well as being a precursor for the synthesis of the steroid hormones
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This note was uploaded on 04/01/2008 for the course CHEM 360 taught by Professor Sharp during the Winter '08 term at University of Michigan.

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STEROIDShandouts - STEROIDS, BILE ACIDS, STEROID HORMONES...

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