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24 Cards in this Set
- Front
- Back
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Structure of Cholesterol
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27 carbons, all from acetyl-CoA
4 Carbon rin gs 8-carbon side chain at C17 3-hydroxy is the only oxygen Double bond between C-5 and C-6 Composed of isoprene |
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What compound do you need to get cholesterol?
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Acetyl-CoA
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How can you get rid of cholesterol?
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Make bile acids or steroids
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Steps in cholesterol biosynthesis
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Acetyl-CoA ---> Acetoacetyl-CoA ---> HMG-CoA ---> Mevalonate ---> Isoprene ---> Squalene ---> Cholesterol
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First step in cholesterol biosynthesis
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Fusion of 2 acetyl-CoA by thiolase
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Rate-limiting step in cholesterol synthesis?
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HMG-CoA reductase, converts HMG-CoA to Mevalonate
Uses NADPH as electron-donor |
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What do statins inhibit?
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They are competitive inhibitors of HMG-CoA reductase
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How do you turn mevalonate into activated isoprene?
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2 sequential phosphorylations on C5 to form pyrophosphate, phosphorylation at C3 followed by immediate decarboxylation and removal of phosphate on C3
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Formation of squalene?
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Isoprenes fuse to form geranyl pyrophosphate and farnesyl pyrophosphate.
2 farnesyl pyrophosphates fuse to form squalene (requires NADP+) |
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Two _________ pyrophosphates fuse to form ______________.
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Two farnesyl pyrophosphates fuse to form squalene.
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What compounds are synthesized from isoprene?
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Cholesterol, Vitamins A, K, E, Dolichol, Carotenoids, bile acids, steroid hormones, vitamin D
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How are plasma levels of cholesterol maintained?
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By de novo synthesis
De novo synthesis is 1 g per day |
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Phosphorylation does what to HMG-CoA reductase?
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decreases its activity
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HMG-CoA reductase is regulated how?
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Stimulated by insulin, inactivated by glucagon, cholesterol stimulates proteolysis of HMG-CoA reductase
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How is ACAT activated?
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By cholesterol
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What does LDL do?
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Puts cholesterol into cells
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What does HDL do?
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HDL goes back to the liver with excess cholesterol
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What are the HDL apolipoproteins?
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ApoA and ApoD
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What are the LDL and VLDL apolipoproteins?
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ApoB-100
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The liver synthesizes 2 primary bile acids:
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chenodeoxycholic acid and cholic acid
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Most bile acids are conjugated via an __________ bond to either ____________ or ____________.
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Most bile acids are conjugated via an AMIDE bond to either TAURINE or GLYCINE.
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Secondary bile acids are:
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7-deoxycholate and lithocholate
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Bile Acid synthesis
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7-alpha-hydroxylase converts cholesterol into 7-hydroxycholesterol
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Feedback control of bile acid synthesis
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Cholesterol will feedforward and activate 7-hydroxylase enzyme
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