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ISU BBMB 405 - The Biosynthesis of Membrane Lipids and Steroids
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BBMB 405 1st Edition Lecture 22 Outline of Last Lecture XVIII. Chapter 26: The Biosynthesis of Membrane Lipids and SteroidsB. Cholesterol is synthesized from acetyl coenzyme A in three stagesC. The complex regulation of cholesterol biosynthesis takes place at several levelsOutline of Current Lecture XVIII. Chapter 26: The Biosynthesis of Membrane Lipids and SteroidsD. Important derivatives of cholesterol include bile salts and steroid hormonesCurrent LectureXVIII. Chapter 26: The Biosynthesis of Membrane Lipids and SteroidsD. Important derivatives of cholesterol include bile salts and steroid hormones1. Handout ¾ and Overhead and Introductiona. 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 strokeb. Statins inhibit cholesterol synthesisc. 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 CoAd. 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 hormonesThese 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.g.h. Glucocorticoids: important in glucohomeostasis, increase gluconeogenesis, anti inflammatory, increase protein degradationi. Mineralocorticoids: maintain sodium balance2. Letters identify the steroid rings and numbers identify carbon atoms3. Steroids are hydroxylated by cytochrome P450 monooxygenases that use NADPH and O24. The cytochrome P450 system is widespread and performs protective function5. Pregnenolone, a precursor for many other steroids, is formed from cholesterol by cleavage of its side chain6. Progesterone and corticosteroids are synthesized from pregnenolone7. Androgens and estrogens are synthesized from pregnenolone8. Vitamin D is derived from cholesterol by ring splitting activity of lighta.b. Vitamin D: not made from cholesterol, not active molecule (have to hydroxylate twice), prevents rickets (when calcium can’t be absorbed)9. Handout 3/6a. Vitamin D promotes absorption of calciumb. Vitamin D is toxic if consume to much: increase calcium absorption, starts precipitating everywhere10. 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


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ISU BBMB 405 - The Biosynthesis of Membrane Lipids and Steroids

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