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Questions and Answers
What is the precursor for cholesterol synthesis?
What is the precursor for cholesterol synthesis?
Where does cholesterol synthesis primarily occur in the body?
Where does cholesterol synthesis primarily occur in the body?
In which form can cholesterol appear in blood lipoproteins?
In which form can cholesterol appear in blood lipoproteins?
What is the active form of vitamin D produced in the skin?
What is the active form of vitamin D produced in the skin?
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What is the relationship between cholesterol concentrations in blood and the development of atherosclerotic vascular disease?
What is the relationship between cholesterol concentrations in blood and the development of atherosclerotic vascular disease?
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What is the main function of cholesterol in the body?
What is the main function of cholesterol in the body?
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Which enzyme phosphorylates HMG-CoA reductase?
Which enzyme phosphorylates HMG-CoA reductase?
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What effect does glucocorticoids have on the activity of HMG-CoA reductase?
What effect does glucocorticoids have on the activity of HMG-CoA reductase?
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Where does most of the biosynthesis of cholesterol occur?
Where does most of the biosynthesis of cholesterol occur?
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What is the primary transporter of cholesterol esters from the liver to the tissues?
What is the primary transporter of cholesterol esters from the liver to the tissues?
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What is the fate of residual cholesterol esters not used by tissues?
What is the fate of residual cholesterol esters not used by tissues?
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What is the primary source of cholesterol for the synthesis of bile acids?
What is the primary source of cholesterol for the synthesis of bile acids?
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Which lipoprotein particles package cholesterol in the intestine?
Which lipoprotein particles package cholesterol in the intestine?
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What is the major rate-limiting step of cholesterol synthesis?
What is the major rate-limiting step of cholesterol synthesis?
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Which lipoprotein particles endocytose LDL?
Which lipoprotein particles endocytose LDL?
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What is the primary function of bile salts produced in the liver?
What is the primary function of bile salts produced in the liver?
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What percentage of bile salts that enter the lumen of the small intestine are eventually excreted in feces?
What percentage of bile salts that enter the lumen of the small intestine are eventually excreted in feces?
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Which test isolates LDL cholesterol and is not affected by mildly to moderately elevated serum triacylglycerol levels?
Which test isolates LDL cholesterol and is not affected by mildly to moderately elevated serum triacylglycerol levels?
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Which protein is involved in reverse cholesterol transport and HDL biogenesis?
Which protein is involved in reverse cholesterol transport and HDL biogenesis?
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What is the main route for cholesterol elimination from the body?
What is the main route for cholesterol elimination from the body?
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Which genetic condition results from a defect in ABCG5 or ABCG8 function?
Which genetic condition results from a defect in ABCG5 or ABCG8 function?
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How does Ezetimibe lower serum cholesterol levels?
How does Ezetimibe lower serum cholesterol levels?
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Which pathway provides NADPH required for cholesterol synthesis?
Which pathway provides NADPH required for cholesterol synthesis?
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What is the committed, rate-limiting step in cholesterol formation?
What is the committed, rate-limiting step in cholesterol formation?
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What is the role of squalene monooxygenase in cholesterol biosynthesis?
What is the role of squalene monooxygenase in cholesterol biosynthesis?
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What is the function of HMG-CoA reductase in cholesterol biosynthesis?
What is the function of HMG-CoA reductase in cholesterol biosynthesis?
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How is the activity of HMG-CoA reductase controlled?
How is the activity of HMG-CoA reductase controlled?
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What is the role of geranyl pyrophosphate and farnesyl pyrophosphate in cholesterol biosynthesis?
What is the role of geranyl pyrophosphate and farnesyl pyrophosphate in cholesterol biosynthesis?
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What activates the carbon 5 and the hydroxyl group on carbon 3 for further reactions in cholesterol biosynthesis?
What activates the carbon 5 and the hydroxyl group on carbon 3 for further reactions in cholesterol biosynthesis?
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What is the first product of the removal of the phosphate group from the C3 hydroxyl group of mevalonate in cholesterol biosynthesis?
What is the first product of the removal of the phosphate group from the C3 hydroxyl group of mevalonate in cholesterol biosynthesis?
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Study Notes
Cholesterol Biosynthesis and HMG-CoA Reductase Regulation
- Phosphate transfers activate carbon 5 and the hydroxyl group on carbon 3 for further reactions in cholesterol biosynthesis.
- Removal of the phosphate group from the C3 hydroxyl group of mevalonate produces Δ3-isopentenyl pyrophosphate, the first of two activated isoprenes for cholesterol synthesis.
- Isoprenes are used for cholesterol biosynthesis, coenzyme Q synthesis, and dolichol synthesis.
- Stage 3 of cholesterol biosynthesis involves the condensation of isopentenyl pyrophosphate and dimethylallyl pyrophosphate to form geranyl pyrophosphate and farnesyl pyrophosphate.
- Geranyl pyrophosphate and farnesyl pyrophosphate are key components in cholesterol biosynthesis and can form covalent bonds with proteins involved in signal transduction.
- Squalene, a compound with 30 carbons, is formed from the fusion of two molecules of farnesyl pyrophosphate.
- Squalene monooxygenase converts squalene into lanosterol, a sterol with the four-ring structure characteristic of the steroid nucleus, which ultimately forms cholesterol.
- HMG-CoA reductase is the rate-limiting step of cholesterol biosynthesis and is the target of cholesterol-lowering drugs called statins.
- Transcriptional regulation of HMG-CoA reductase is controlled by sterol-regulatory element-binding proteins (SREBPs) that directly activate the expression of genes dedicated to cholesterol synthesis.
- Rising levels of cholesterol and bile salts may change the oligomerization state of HMG-CoA reductase, rendering the enzyme more susceptible to ubiquitination and proteolysis, decreasing its activity.
- HMG-CoA reductase is also regulated by phosphorylation and dephosphorylation, with glucagon inactivating the enzyme and hyperinsulinemia increasing its activity.
- The regulation of HMG-CoA reductase activity is controlled through transcriptional regulation, proteolytic degradation, and covalent modification.
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Description
Test your knowledge of cholesterol biosynthesis and the regulation of HMG-CoA reductase with this quiz. Explore the key stages and components involved in cholesterol synthesis, as well as the mechanisms that control the activity of HMG-CoA reductase, the rate-limiting enzyme in this process.
