cholesterol biosynthesis

cholesterol biosynthesis - Cholesterol Biosynthesis Uses of...

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Unformatted text preview: Cholesterol Biosynthesis Uses of Cholesterol (Review) Membranes, crucial component Precursor for bile acids, solubilizes lipids in intestines Precursor to steroid hormones Precursor to vitamin D *Synthesis mostly in liver* Cholesterol Biosynthesis-Overview a a ' b b b 3C 2 C 6 C' 6 C 5 C 10 C 15 C 30 cholesterol a. HMG-CoA synthase is common to sterol and ketone body synthesis a ' . HMG-CoA reductase makes mevalonate (MVA), the key and first intermediate of sterol biosynthesis. This is a highly regulated step. b. An active isoprene is made which may combine with another C 5 unit to make C 10 and C 15 products. 3C 2 C 6 C' 6 C 5 C 10 c d C 15 C 30 cholesterol c. Two C 15 units dimerize to form squalene , a C 30 molecule. d. Squalene is cyclized using O 2 and many enzymes to give cholesterol . --The whole process is very energy dependent in terms of ATP and NADPH utilization-- Mevalonate Pathway for Cholesterol Biosynthesis Mevalonate is synthesized via HMG-CoA synthase 3C2 C 6 1. Condensation of two acetyl- CoA 2. Add another acetyl from acetyl-CoA 3. Beta-hydroxy-beta methylglutaryl-CoA reductase (HMG-CoA reductase) makes mevalonate; it is the rate limiting step & key regulation step of cholesterol synthesis Lehn fig 21-34 Three kinases and a decarboxylase X 3 X 3 Lehn fig 21-35 isoprene Isoprene is made from mevalonate C6 C5 3 ATPs & decarboxylation needed to produce 2 activated isoprene molecules 2 isoprene units join head-to-tail to form geranyl pyrophosphate (C10) pyrophosphate hydrolysis drives rxn. another isoprene is added head to tail to form farnesyl pyrophosphate (C15) pyrophosphate hydrolysis drives rxn. b oth rxns catalyzed by prenyl transferase 2 farnesyl units joined head-to-head to form squalene (C30) e nzyme = squalene synthase reduction with NADPH & 2 pyrophosphates released Lehn fig 21-37 squalene monooxygenase...
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cholesterol biosynthesis - Cholesterol Biosynthesis Uses of...

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