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Questions and Answers
What is the primary form of cholesterol found in plasma lipoproteins?
Which hormone is responsible for stimulating the phosphorylation and inactivation of HMG-CoA reductase?
What role does insulin play in the regulation of cholesterol biosynthesis?
What is an effect of reduced intracellular cholesterol concentration on cholesterol biosynthesis?
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What type of enzyme is acyl-CoA-cholesterol acyl transferase (ACAT)?
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What is the primary role of acyl-CoA synthase in triacylglycerol metabolism?
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Which compound is produced from the action of acyltransferase on glycerol-P?
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What is the significance of CoA in the synthesis of triacylglycerols?
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Which metabolic pathway is directly linked to the degradation of triacylglycerols?
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What is the result of the complete hydrolysis of triacylglycerols?
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What is the role of malonyl-CoA in fatty acid synthesis?
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Which component of fatty acid synthase is responsible for binding malonyl-CoA and acetyl-CoA?
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What occurs during the first step of fatty acid synthesis?
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Which process contributes to the release of CO2 during fatty acid synthesis?
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What is the main product synthesized from the combination of acetyl-CoA and malonyl-CoA?
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Which enzyme is responsible for the formation of malonyl-CoA from acetyl-CoA?
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What is the significance of the acyl carrier protein (ACP) in fatty acid synthase?
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What type of reaction primarily occurs when malonyl-CoA combines with acetyl-CoA?
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Which of the following statements about fatty acid synthase is true?
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What is released as a byproduct during the condensation reaction of acetyl-CoA and malonyl-CoA?
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Study Notes
Triacylglycerol Metabolism
- Acyl-CoA synthetase catalyzes the synthesis of acyl-CoA from fatty acids.
- Acyl-CoA acyltransferase is involved in the formation of triacylglycerols (TAG) from glycerol-3-phosphate.
- Lipases hydrolyze triacylglycerols to release fatty acids and glycerol for energy metabolism.
- Glycerol-3-phosphate is derived from glucose via glycolysis.
Formation of Triacylglycerols
- Acyl-CoA reacts with glycerol-3-phosphate to form phosphatidic acid, an intermediate in lipid synthesis.
- Phosphatidic acid is converted to diacylglycerol (DAG) through the action of a phosphatase.
- DAG can further react with acyl-CoA to form triacylglycerol, the main storage form of lipids.
Cholesterol Metabolism
- Acyl-CoA cholesterol acyltransferase (ACAT) converts free cholesterol into cholesteryl esters, making it hydrophobic for easier storage within lipoproteins.
- Cholesteryl esters constitute approximately 70% of the cholesterol found in plasma lipoproteins.
Regulation of Cholesterol Biosynthesis
- Cholesterol synthesis is regulated hormonally and transcriptionally at the level of HMG-CoA reductase.
- Insulin activates HMG-CoA reductase through dephosphorylation, promoting cholesterol synthesis.
- Glucagon inhibits HMG-CoA reductase by promoting its phosphorylation, reducing cholesterol synthesis.
Fatty Acid Synthesis
- Fatty acid synthesis begins with the formation of malonyl-CoA from acetyl-CoA, a reaction catalyzed by acetyl-CoA carboxylase.
- The first step in fatty acid chain elongation is the condensation of acetyl groupt and malonyl group with the release of CO2.
Fatty Acid Oxidation
- Glucagon promotes the mobilization of fatty acids from triacylglycerol stores for energy, while insulin aids in their synthesis.
- Malonyl-CoA inhibits carnitine acyltransferase I (CPT I), preventing fatty acid entry into mitochondria during high carbohydrate intake.
- β-oxidation in mitochondria breaks down fatty acids to generate acetyl-CoA for energy production.
Coordination of Fatty Acid Metabolism
- High carbohydrate meals stimulate insulin release, leading to enhanced fatty acid synthesis and reduced degradation.
- Insulin activates ACC, which produces malonyl-CoA, inhibiting CPT I and subsequently β-oxidation, focusing on lipid storage rather than degradation.
Key Enzymes and Processes
- ACAT: Catalyzes transfer of fatty acids to cholesterol.
- HMG-CoA reductase: Central to cholesterol biosynthesis, regulated by hormonal signals.
- Acetyl-CoA Carboxylase: Regulates the first step of fatty acid synthesis.
- Protein phosphatase 1: Activates ACC, linking insulin signaling to lipid metabolism.
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Description
This quiz covers key aspects of triacylglycerol and cholesterol metabolism, including the roles of acyl-CoA synthetase, lipases, and the formation of triacylglycerols from glycerol-3-phosphate. It also explores the conversion of free cholesterol into cholesteryl esters for storage. Test your knowledge on these vital biochemical processes!
