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Questions and Answers
What is the primary physiological role of the lipid metabolic pathways described in the learning objectives?
What is the primary physiological role of the lipid metabolic pathways described in the learning objectives?
- To provide energy for the brain and nervous system
- To facilitate the storage and mobilization of fat in the body (correct)
- To maintain homeostasis of blood lipid levels
- To regulate the synthesis and breakdown of cholesterol
Which of the following best describes the relationship between fatty acid synthesis and oxidation?
Which of the following best describes the relationship between fatty acid synthesis and oxidation?
- They are independent processes that occur simultaneously
- Synthesis occurs in the cytoplasm while oxidation occurs in the mitochondria
- Physiological conditions that promote synthesis largely inhibit oxidation, and vice versa (correct)
- They are mutually exclusive processes that cannot occur together
What is the significance of the carnitine shuttle in the beta-oxidation process?
What is the significance of the carnitine shuttle in the beta-oxidation process?
- It generates acetyl-CoA from the breakdown of fatty acids
- It regulates the rate of fatty acid synthesis in the cytoplasm
- It transports fatty acids from the cytoplasm into the mitochondria for oxidation (correct)
- It converts ketone bodies back into acetyl-CoA for energy production
What is the significance of ketone bodies in the context of lipid metabolism?
What is the significance of ketone bodies in the context of lipid metabolism?
Which of the following best describes the relationship between acetyl-CoA and the lipid metabolic pathways discussed in the learning objectives?
Which of the following best describes the relationship between acetyl-CoA and the lipid metabolic pathways discussed in the learning objectives?
Where does de novo synthesis of fatty acids mainly occur?
Where does de novo synthesis of fatty acids mainly occur?
What is the primary end product of de novo fatty acid synthesis?
What is the primary end product of de novo fatty acid synthesis?
Which tissues can synthesize fatty acids in small quantities, along with liver cells?
Which tissues can synthesize fatty acids in small quantities, along with liver cells?
What is the key substrate for de novo fatty acid synthesis?
What is the key substrate for de novo fatty acid synthesis?
Which type of fatty acids can brain cells produce for the synthesis of brain phospholipids?
Which type of fatty acids can brain cells produce for the synthesis of brain phospholipids?
What process is needed for the desaturation of long-chain fatty acids to produce polyunsaturated fatty acids?
What process is needed for the desaturation of long-chain fatty acids to produce polyunsaturated fatty acids?
What is the end product of fatty acid synthesis driven by the enzyme fatty acid synthase (FAS)?
What is the end product of fatty acid synthesis driven by the enzyme fatty acid synthase (FAS)?
Which pathway provides the reductant NADPH required for fatty acid synthesis?
Which pathway provides the reductant NADPH required for fatty acid synthesis?
What is the caloric value per unit mass of triacylglycerols compared to carbohydrates and proteins?
What is the caloric value per unit mass of triacylglycerols compared to carbohydrates and proteins?
What effect does the presence of unsaturated fatty acids in triacylglycerols have on their melting temperature (Tm)?
What effect does the presence of unsaturated fatty acids in triacylglycerols have on their melting temperature (Tm)?
Where do the carbons for fatty acid synthesis come from directly?
Where do the carbons for fatty acid synthesis come from directly?
How are newly synthesized fatty acids primarily stored?
How are newly synthesized fatty acids primarily stored?
What is the primary source of mitochondrial acetyl CoA?
What is the primary source of mitochondrial acetyl CoA?
How is the acetyl group of acetyl CoA transported from the mitochondrial matrix to the cytosol?
How is the acetyl group of acetyl CoA transported from the mitochondrial matrix to the cytosol?
What enzyme catalyzes the conversion of citrate to oxaloacetate and acetyl CoA in the cytosol?
What enzyme catalyzes the conversion of citrate to oxaloacetate and acetyl CoA in the cytosol?
What is the rate-limiting and regulated step in fatty acid synthesis?
What is the rate-limiting and regulated step in fatty acid synthesis?
Which of the following is an allosteric activator of acetyl CoA carboxylase (ACC)?
Which of the following is an allosteric activator of acetyl CoA carboxylase (ACC)?
Which vitamin is required for the carboxylation of acetyl CoA to malonyl CoA?
Which vitamin is required for the carboxylation of acetyl CoA to malonyl CoA?
Which of the following statements about ketone bodies is correct?
Which of the following statements about ketone bodies is correct?
Which of the following tissues/cells can utilize ketone bodies as an energy source when their concentrations are high?
Which of the following tissues/cells can utilize ketone bodies as an energy source when their concentrations are high?
What is the primary role of ketone bodies during fasting or prolonged exercise?
What is the primary role of ketone bodies during fasting or prolonged exercise?
Which of the following statements about ketogenesis is correct?
Which of the following statements about ketogenesis is correct?
What happens to the ketone bodies produced by the liver during fasting or prolonged exercise?
What happens to the ketone bodies produced by the liver during fasting or prolonged exercise?
Which of the following is true regarding the production of ketone bodies in the liver?
Which of the following is true regarding the production of ketone bodies in the liver?
What is the common compound that fatty acids are both synthesized from and oxidized to?
What is the common compound that fatty acids are both synthesized from and oxidized to?
In which cellular compartment are fatty acids primarily oxidized?
In which cellular compartment are fatty acids primarily oxidized?
Under what physiological conditions is fatty acid synthesis largely inhibited?
Under what physiological conditions is fatty acid synthesis largely inhibited?
Which organelle is primarily responsible for the synthesis of fatty acids?
Which organelle is primarily responsible for the synthesis of fatty acids?
What process prevents the wasteful cycling between fatty acid synthesis and oxidation?
What process prevents the wasteful cycling between fatty acid synthesis and oxidation?
Which tissues are primarily responsible for de novo fatty acid synthesis?
Which tissues are primarily responsible for de novo fatty acid synthesis?
Which of the following is the primary end product of de novo fatty acid synthesis?
Which of the following is the primary end product of de novo fatty acid synthesis?
What is the key substrate required for de novo fatty acid synthesis?
What is the key substrate required for de novo fatty acid synthesis?
Which process is required for the production of polyunsaturated fatty acids (PUFAs) from saturated fatty acids?
Which process is required for the production of polyunsaturated fatty acids (PUFAs) from saturated fatty acids?
Which of the following is NOT a source of substrates for de novo fatty acid synthesis?
Which of the following is NOT a source of substrates for de novo fatty acid synthesis?
Which cofactors are required for de novo fatty acid synthesis?
Which cofactors are required for de novo fatty acid synthesis?
What is the primary end product of de novo fatty acid synthesis driven by the enzyme fatty acid synthase (FAS)?
What is the primary end product of de novo fatty acid synthesis driven by the enzyme fatty acid synthase (FAS)?
Which pathway provides the reductant NADPH required for fatty acid synthesis?
Which pathway provides the reductant NADPH required for fatty acid synthesis?
How are newly synthesized fatty acids primarily stored?
How are newly synthesized fatty acids primarily stored?
What effect does the presence of unsaturated fatty acids in triacylglycerols have on their melting temperature (Tm)?
What effect does the presence of unsaturated fatty acids in triacylglycerols have on their melting temperature (Tm)?
Which tissues/cells can synthesize fatty acids in small quantities, along with the liver?
Which tissues/cells can synthesize fatty acids in small quantities, along with the liver?
Which enzyme is responsible for the release of fatty acids from triacylglycerols (TAGs) in adipose tissue during lipolysis?
Which enzyme is responsible for the release of fatty acids from triacylglycerols (TAGs) in adipose tissue during lipolysis?
What is the primary role of the carnitine shuttle in fatty acid oxidation?
What is the primary role of the carnitine shuttle in fatty acid oxidation?
Which of the following is a product of each cycle of fatty acid β-oxidation?
Which of the following is a product of each cycle of fatty acid β-oxidation?
What is the primary function of malonyl-CoA in the regulation of fatty acid metabolism?
What is the primary function of malonyl-CoA in the regulation of fatty acid metabolism?
Which of the following amino acids is a precursor for carnitine biosynthesis?
Which of the following amino acids is a precursor for carnitine biosynthesis?
Which of the following best describes the relationship between fatty acid synthesis and β-oxidation?
Which of the following best describes the relationship between fatty acid synthesis and β-oxidation?
What is the fate of acetone produced during ketogenesis in the liver?
What is the fate of acetone produced during ketogenesis in the liver?
What is the total number of ATP molecules produced from the complete oxidation of one molecule of palmitoyl CoA (16 carbons)?
What is the total number of ATP molecules produced from the complete oxidation of one molecule of palmitoyl CoA (16 carbons)?
Which of the following is the correct sequence of events in the conversion of acetyl CoA from fatty acid oxidation to ketone bodies?
Which of the following is the correct sequence of events in the conversion of acetyl CoA from fatty acid oxidation to ketone bodies?
Which of the following tissues cannot utilize ketone bodies as an alternative fuel source?
Which of the following tissues cannot utilize ketone bodies as an alternative fuel source?
What is the primary role of ketone bodies during prolonged fasting or starvation?
What is the primary role of ketone bodies during prolonged fasting or starvation?
Study Notes
Lipid Metabolic Pathways
- Fatty acids are synthesized from and oxidized to a common compound: Acetyl-CoA
- Physiological conditions that promote FA synthesis largely inhibit oxidation, and vice versa (preventing futile cycling)
De Novo Synthesis of Fatty Acids
- Occurs mainly in the cytosol of liver cells, mammary glands, and adipose tissue cells
- Substrates: excess carbohydrates and proteins from the diet that exceed the body's needs
- Acetyl Coenzyme A (ACoA) from mitochondria is key
- Primary product: palmitate or palmitic acid (16 C)
- Can be further elongated in smooth endoplasmic reticulum (sER)
- Brain cells can produce very long FA required for synthesis of brain phospholipids
- Certain enzymes in sER can cause desaturation of LCFA by adding cis double bonds
- A variety of polyunsaturated FA (PUFA) can be produced by desaturation + elongation
Storage of Lipids
- Lipids are stored as triacylglycerol (TAG) in adipose tissue cells (adipocytes)
- Three FA in TAG are generally not the same type: C-1 often saturated, C-2 unsaturated, C-3 either
- Presence of unsaturated FA decreases the Tm of the lipid
- Newly synthesized fatty acids can be stored as mono-, di-, or triacylglycerols
- Lipids caloric value per unit mass is over twice as great as carbs and proteins
Mobilization of Fats (from Adipose Tissue)
- Requires release from their TAG form → lipolysis
- With help of Hormone-Sensitive Lipase (HSL) (stimulated by epinephrine and glucagon)
Fatty Acid β-Oxidation
- Major pathway for FA catabolism → occurs in the mitochondria
- Long chain fatty acids must form an active intermediate (fatty acyl CoA) before being oxidized inside the mitochondria
- The carnitine shuttle is required to transport fatty-acyl-CoA into the mitochondria (rate limiting transport)
Carnitine Shuttle
- Carnitine is synthesized from amino acids lysine and methionine in liver and kidneys (abundant in mitochondrial membranes of muscle tissue)
- Carnitine can be taken up from the diet (mainly from animal products)
- Carnitine deficiencies cause decreased ability of tissues to use LCFA as fuel
- Carnitine shuttle (CPT1) can be inhibited by malonyl CoA, so newly synthesized FA cannot be transferred into mitochondria to be degraded
β-Oxidation Process
- Cyclic process, each cycle is catalyzed by enzymes with chain length specificity
- Each cycle produces: 1 acetyl-CoA + 1 NADH + 1 FADH2
- First cycle of β-oxidation: a sequence of four reactions that involve the β-carbon and cause the shortening of the FA by two carbons at the carboxyl end.
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Description
Test your knowledge on lipid metabolic pathways, including de novo synthesis of fatty acids, beta-oxidation, ketolysis, mobilization of fats, and ketone bodies. Explore the role of carnitine shuttle in beta-oxidation and understand the process of ketolysis.
