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Questions and Answers
Where do ketone bodies diffuse from?
Where do ketone bodies diffuse from?
What is the fate of acetone in the body?
What is the fate of acetone in the body?
What is the precursor molecule required for cholesterol synthesis?
What is the precursor molecule required for cholesterol synthesis?
Which enzyme catalyzes the conversion of HMG-CoA to mevalonic acid?
Which enzyme catalyzes the conversion of HMG-CoA to mevalonic acid?
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Where is the subcellular location of cholesterol synthesis?
Where is the subcellular location of cholesterol synthesis?
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What is the function of cholesterol synthesis?
What is the function of cholesterol synthesis?
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Which organs make the largest contributions to the body's cholesterol pool?
Which organs make the largest contributions to the body's cholesterol pool?
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What is the role of cholesterol in the body?
What is the role of cholesterol in the body?
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Where is the reaction of converting acetyl-CoA to HMG-CoA located?
Where is the reaction of converting acetyl-CoA to HMG-CoA located?
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What is the product of the reaction catalyzed by HMG-CoA reductase?
What is the product of the reaction catalyzed by HMG-CoA reductase?
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Study Notes
Metabolism of Lipids
- Covers key aspects such as digestion, degradation, biosynthesis, eicosanoids, ketone bodies, and cholesterol metabolism.
Digestion of Dietary Lipids
- Lipids aggregate in large droplets in watery environments, requiring emulsification to form smaller droplets for digestion.
- Mechanical breakdown occurs in the mouth and stomach primarily through chewing and churning.
- Lingual and gastric lipases contribute limited digestion of triacylglycerol before reaching the small intestine.
- Most lipid digestion occurs in the small intestine by pancreatic lipase, stimulated by the presence of fat.
Role of Bile in Digestion
- Bile acids, synthesized from cholesterol, play a crucial role in emulsifying fats.
- Bile salts, made from bile acids in the liver and stored in the gallbladder, are secreted in response to cholecystokinin, aiding in digestion.
Digestion and Absorption Processes
- Triacylglycerols (TG) are broken down into two free fatty acids and monoacylglycerol (2MG) by pancreatic lipases.
- Phospholipids are hydrolyzed to lysophospholipids by phospholipases A2.
- Cholesterol esters are converted to free cholesterol by cholesterol esterase.
- Absorbed lipid digestion products are re-esterified and packaged into chylomicrons for safe circulation.
Lipolysis: Breakdown of Triglycerides
- Lipolysis is the process that breaks down TG into glycerol and free fatty acids, occurring in the cytosol of adipose tissue.
- Hormone-sensitive lipase facilitates lipolysis and is stimulated by glucagon and epinephrine, while inhibited by insulin.
Fates of Lipolysis Products
- Glycerol enters the liver for glycolysis and gluconeogenesis due to lack of glycerol kinase in adipocytes.
- Free fatty acids can be re-esterified into TG or released into the bloodstream for transport and oxidation by tissues.
Fatty Acid Oxidation (β-Oxidation)
- Fatty acids must be activated to fatty acyl-CoA before entering the mitochondrial matrix for β-oxidation.
- This process repeats until the fatty acid is fully converted into acetyl-CoA, producing NADH and FADH2.
Energy Yield from β-Oxidation
- Each β-oxidation cycle generates acetyl-CoA, which is further utilized in the TCA cycle to produce ATP, CO2, and H2O.
- Odd-numbered fatty acids produce propionyl-CoA, which is converted into succinyl-CoA.
Ketone Body Metabolism
- Ketone bodies, produced in the liver, are transported to peripheral tissues and converted back into acetyl-CoA, generating NADH.
- Acetone is unable to revert to acetyl-CoA and is excreted in urine.
Cholesterol Biosynthesis
- Cholesterol synthesis initiates with acetyl-CoA, converted to HMG-CoA, and then to mevalonic acid through HMG-CoA reductase, the key regulatory step.
- The synthesis occurs in the cytosol and endoplasmic reticulum of tissues, primarily the liver, intestine, adrenal cortex, and reproductive organs.
Importance of Cholesterol
- Cholesterol is essential for cellular membrane structure and is found in all animal tissues.
- It also serves as a precursor for bile salts and steroid hormones, playing a vital role in physiological processes.
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Description
This quiz covers the metabolism of lipids, including the digestion of dietary lipids, lipid degradation, lipid biosynthesis, eicosanoids biosynthesis, and the metabolism of ketone bodies and cholesterol. It is a comprehensive quiz for biochemistry students.
