BBMB 405 1st Edition Lecture 22 Outline of Last Lecture XVIII Chapter 26 The Biosynthesis of Membrane Lipids and Steroids B Cholesterol is synthesized from acetyl coenzyme A in three stages C The complex regulation of cholesterol biosynthesis takes place at several levels Outline of Current Lecture XVIII Chapter 26 The Biosynthesis of Membrane Lipids and Steroids D Important derivatives of cholesterol include bile salts and steroid hormones Current Lecture XVIII Chapter 26 The Biosynthesis of Membrane Lipids and Steroids D Important derivatives of cholesterol include bile salts and steroid hormones 1 Handout and Overhead and Introduction a Etiology of Atherosclerosis LDL LDLox macrophage foam cells in artery trapped in arterial wall smooth muscle proliferation plaque in lumen artery narrows forms clot heart attack or stroke b Statins inhibit cholesterol synthesis c Bile acid synthesis Cholesterol Cholyl CoA 7 alpha Hydroxylase vitamin C dependent Epimerization of 3 beta OH to 3 alpha OH Reduction of delta5 double bond Hydroxylation of C12 bond Removal of 3 carbons from tail as propionyl CoA d Cholyl CoA Glycine Glycocholate detergent in bile e Cholyl CoA Taurine Taurocholate detergent in bile f We can t burn cholesterol to carbon dioxide so we excrete or convert to steroid hormones These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 2 3 4 5 6 g h Glucocorticoids important in glucohomeostasis increase gluconeogenesis anti inflammatory increase protein degradation i Mineralocorticoids maintain sodium balance Letters identify the steroid rings and numbers identify carbon atoms Steroids are hydroxylated by cytochrome P450 monooxygenases that use NADPH and O 2 The cytochrome P450 system is widespread and performs protective function Pregnenolone a precursor for many other steroids is formed from cholesterol by cleavage of its side chain Progesterone and corticosteroids are synthesized from pregnenolone 7 Androgens and estrogens are synthesized from pregnenolone 8 Vitamin D is derived from cholesterol by ring splitting activity of light a b Vitamin D not made from cholesterol not active molecule have to hydroxylate twice prevents rickets when calcium can t be absorbed 9 Handout 3 6 a Vitamin D promotes absorption of calcium b Vitamin D is toxic if consume to much increase calcium absorption starts precipitating everywhere 10 Ethanol metabolism p 544 Handout 3 6 not sure if this will be on exam body can adapt to excessive ethanol intake by degrading ethanol through a different pathway THIQ hypothesis
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