Post-absorption Processing of Lipids
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Questions and Answers

Which type of dietary fat is primarily found in oils from fish and plants?

  • Hydrogenated fats
  • Saturated fats
  • Unsaturated fats (correct)
  • Trans fats

    • What is the main structural feature of triglycerides?

  • Three fatty acids attached to a glycerol backbone (correct)
  • One glycerol backbone and one fatty acid
  • One fatty acid and one glycerol
  • Three glycerol molecules attached to a fatty acid

    • Which process occurs primarily in the liver to produce energy from fatty acids?

  • Beta-oxidation
  • Ketogenesis (correct)
  • Triglyceride synthesis
  • Lipolysis

    • What are apolipoproteins NOT involved in?

    <p>Regulating digestion of carbohydrates</p> Signup and view all the answers

    What is the primary energy source stored in adipocytes?

    <p>Triglycerides</p> Signup and view all the answers

    What is the main function of lipoproteins in the body?

    <p>Transport lipid molecules in water</p> Signup and view all the answers

    Which statement about beta-oxidation is incorrect?

    <p>It is the synthesis of triglycerides from fatty acids.</p> Signup and view all the answers

    Which of the following is an important function of brown adipose tissue?

    <p>Production of heat through thermogenesis</p> Signup and view all the answers

    What is the primary function of lipoprotein lipase (LPL) in the body?

    <p>To hydrolyze triglycerides into fatty acids and monoacylglycerol</p> Signup and view all the answers

    Which enzyme initiates the breakdown of triglycerides during lipolysis in adipocytes?

    <p>Adipose triglyceride lipase (ATGL)</p> Signup and view all the answers

    What happens to triglycerides in the fed state?

    <p>They are transported in chylomicrons to adipose tissue for storage</p> Signup and view all the answers

    In which part of the cell does the activation of fatty acids to acyl-CoA occur?

    <p>Cytosol</p> Signup and view all the answers

    Which hormone primarily inhibits lipolysis in adipocytes?

    <p>Insulin</p> Signup and view all the answers

    What role do chylomicrons play in lipid transport?

    <p>They carry triglycerides from the intestines to peripheral tissues</p> Signup and view all the answers

    What is the process by which fatty acids are broken down to generate energy called?

    <p>β-oxidation</p> Signup and view all the answers

    Which of the following is NOT a major component of chylomicrons?

    <p>Free amino acids</p> Signup and view all the answers

    During which metabolic state are triglycerides preferentially taken up by muscle cells?

    <p>Fasting state</p> Signup and view all the answers

    Which factor is crucial for the hormonal regulation of hormone-sensitive lipase (HSL)?

    <p>Phosphorylation state</p> Signup and view all the answers

    What process occurs after triglycerides have been hydrolyzed by lipoprotein lipase (LPL)?

    <p>They diffuse into adipocytes and are reassembled into triglycerides</p> Signup and view all the answers

    Which molecules are involved in the transport of free fatty acids in the bloodstream?

    <p>Albumin</p> Signup and view all the answers

    Which of the following statements about the synthesis of triglycerides is FALSE?

    <p>Triglycerides are synthesized only during fasting.</p> Signup and view all the answers

    What happens to glycerol released during lipolysis?

    <p>It travels to the liver for metabolism into glycolysis or gluconeogenesis.</p> Signup and view all the answers

    What is the primary function of ketone bodies during fasting?

    <p>To serve as a reserve fuel for energy, particularly for the brain</p> Signup and view all the answers

    Which enzyme is responsible for regenerating acyl-CoA from acyl-carnitine in the mitochondrion?

    <p>Carnitine Palmitoyl Transferase II</p> Signup and view all the answers

    What accumulates in the blood during Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD)?

    <p>Medium-chain fatty acids</p> Signup and view all the answers

    What effect does Malonyl-CoA have on fatty acid transport into the mitochondria?

    <p>It inhibits the activity of CPT I preventing fatty acid entry</p> Signup and view all the answers

    What is the role of Uncoupling Protein 1 (UCP1) in brown adipose tissue?

    <p>To facilitate the production of heat instead of ATP</p> Signup and view all the answers

    During which metabolic state is ketogenesis primarily stimulated?

    <p>When blood glucose is low and glycogen stores are depleted</p> Signup and view all the answers

    What is one potential consequence of ketoacidosis if left unmanaged?

    <p>Severe dehydration and confusion</p> Signup and view all the answers

    Which type of fatty acids can diffuse directly into the mitochondrion?

    <p>Short-chain fatty acids</p> Signup and view all the answers

    What is the primary metabolic function of brown adipose tissue (BAT)?

    <p>Production of heat through thermogenesis</p> Signup and view all the answers

    What triggers the switch from fatty acid breakdown to ketogenesis?

    <p>Depletion of oxaloacetate due to low glucose</p> Signup and view all the answers

    What is a common clinical sign of Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD)?

    <p>Intolerance to prolonged fasting</p> Signup and view all the answers

    Which of the following compounds is formed during the first step of β-oxidation?

    <p>Acyl-CoA</p> Signup and view all the answers

    What is one of the key benefits of a ketogenic diet?

    <p>Reduction in visceral fat</p> Signup and view all the answers

    How does brown adipose tissue primarily differ from white adipose tissue?

    <p>It produces heat rather than synthesizing ATP</p> Signup and view all the answers

    What is the primary route for fatty acids to enter adipocytes after being transported via chylomicrons?

    <p>Diffusion across the cell membrane</p> Signup and view all the answers

    Which enzyme is responsible for the phosphorylation and activation of Hormone-Sensitive Lipase during a fasting state?

    <p>Protein Kinase A</p> Signup and view all the answers

    What fate does glycerol have after being released during the breakdown of triglycerides?

    <p>Transported to the liver for metabolism</p> Signup and view all the answers

    During β-oxidation, which molecule is produced at the end of each complete cycle?

    <p>Acetyl-CoA</p> Signup and view all the answers

    What is the primary method of transport for free fatty acids in the bloodstream after lipolysis?

    <p>Bound to albumin</p> Signup and view all the answers

    Which component of β-oxidation is responsible for the cleavage of ketoacyl-CoA to release Acetyl-CoA?

    <p>Beta-Ketothiolase</p> Signup and view all the answers

    What triggers the activation of carnitine shuttle components during fatty acid metabolism?

    <p>Elevation of acyl-CoA levels</p> Signup and view all the answers

    What event occurs during the re-esterification of fatty acids in adipocytes?

    <p>Fatty acids are combined with glycerol to form triglycerides.</p> Signup and view all the answers

    What is the immediate destination of chylomicrons after they are secreted across the basolateral membrane?

    <p>Into the lymphatic circulation</p> Signup and view all the answers

    Where do chylomicrons ultimately enter the bloodstream?

    <p>Via the left subclavian vein</p> Signup and view all the answers

    Which process is directly involved in the movement of chylomicrons from the intestines to the circulatory system?

    <p>Exocytosis</p> Signup and view all the answers

    What is the pathway followed by chylomicrons after they are formed in the intestinal mucosa?

    <p>Lymphatic system to blood circulation</p> Signup and view all the answers

    What type of transport mechanism is involved when chylomicrons cross the basolateral membrane of intestinal cells?

    <p>Transcytosis</p> Signup and view all the answers

    What is the primary function of chylomicrons in the body?

    <p>Transport triglycerides from the intestines to adipose tissue</p> Signup and view all the answers

    What enzyme is responsible for the hydrolysis of triglycerides in chylomicrons at the adipose tissue?

    <p>Lipoprotein lipase (LPL)</p> Signup and view all the answers

    In the fed state, what happens to triglycerides transported by chylomicrons?

    <p>They are stored in adipose tissue as triglycerides</p> Signup and view all the answers

    During fasting or exercise, what hormonal changes trigger the mobilization of triglycerides?

    <p>Low insulin, high glucagon and catecholamines</p> Signup and view all the answers

    What is the role of hormone-sensitive lipase (HSL) during fasting?

    <p>Hydrolyzes triglycerides into free fatty acids and glycerol</p> Signup and view all the answers

    Where are chylomicrons synthesized within the intestinal cells?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    After secretion from enterocytes, chylomicrons enter the lymphatic system through which structure?

    <p>Thoracic duct</p> Signup and view all the answers

    What process occurs to extract energy from free fatty acids?

    <p>Beta-oxidation</p> Signup and view all the answers

    Which of the following statements about glycerol is correct?

    <p>Glycerol is transported to the liver for glycolysis or gluconeogenesis.</p> Signup and view all the answers

    What triggers the phosphorylation and activation of hormone-sensitive lipase (HSL)?

    <p>Increased glucagon and catecholamines</p> Signup and view all the answers

    Which of the following statements about chylomicrons is correct?

    <p>Chylomicrons enter the bloodstream via the thoracic duct.</p> Signup and view all the answers

    During fasting, which of the following hormones primarily promotes lipolysis?

    <p>Glucagon</p> Signup and view all the answers

    What triggers the activation of hormone-sensitive lipase (HSL)?

    <p>Phosphorylation by protein kinases</p> Signup and view all the answers

    Which statement accurately describes β-oxidation?

    <p>It is the process of breaking down fatty acids to produce acetyl-CoA.</p> Signup and view all the answers

    What is the primary fate of glycerol released from triglyceride breakdown?

    <p>It is converted to glucose in the liver.</p> Signup and view all the answers

    What happens to free fatty acids that diffuse into adipocytes?

    <p>They are converted back into triglycerides for storage.</p> Signup and view all the answers

    Which of the following is NOT a source of glycerol for triglyceride synthesis in adipose tissue?

    <p>Ketone body metabolism</p> Signup and view all the answers

    What is required for fatty acids to be activated before they can enter the β-oxidation pathway?

    <p>Conversion to acyl-CoA</p> Signup and view all the answers

    During β-oxidation, what is the main product produced from the breakdown of a fatty acid?

    <p>Acetyl-CoA</p> Signup and view all the answers

    Which of the following enzymes is involved in the initial step of β-oxidation?

    <p>Acyl-CoA dehydrogenase</p> Signup and view all the answers

    What is the primary enzyme that facilitates the uptake of triglycerides from chylomicrons into adipocytes?

    <p>Lipoprotein lipase (LPL)</p> Signup and view all the answers

    What is the effect of insulin on hormone-sensitive lipase (HSL)?

    <p>Insulin inhibits the phosphorylation of HSL.</p> Signup and view all the answers

    What is the primary role of carnitine in fatty acid metabolism?

    <p>It transports fatty acids into the mitochondria.</p> Signup and view all the answers

    Which of the following statements about lipolysis is correct?

    <p>It leads to the production of glucose from glycerol.</p> Signup and view all the answers

    What is the primary function of acyl-CoA synthetase in fatty acid metabolism?

    <p>To activate fatty acids for β-oxidation</p> Signup and view all the answers

    Where does β-oxidation primarily occur in the cell?

    <p>Mitochondria</p> Signup and view all the answers

    What is the function of carnitine acyltransferase I in fatty acid metabolism?

    <p>To convert acyl-CoA to acyl-carnitine</p> Signup and view all the answers

    What is the primary enzyme involved in the re-esterification of free fatty acids and glycerol to form triglycerides in adipocytes?

    <p>Diacylglycerol acyltransferase (DGAT)</p> Signup and view all the answers

    How do free fatty acids primarily travel in the bloodstream to reach target tissues?

    <p>Bound to albumin</p> Signup and view all the answers

    What is the effect of insulin on lipogenesis in adipose tissue?

    <p>It promotes lipogenesis by stimulating the synthesis of fatty acids.</p> Signup and view all the answers

    What is one major fate of Acetyl-CoA produced from β-oxidation of fatty acids?

    <p>It enters the Krebs cycle for energy production.</p> Signup and view all the answers

    Which hormone primarily promotes lipolysis in adipose tissue?

    <p>Glucagon</p> Signup and view all the answers

    What is the initial step in the digestion of dietary lipids?

    <p>Emulsification by bile salts</p> Signup and view all the answers

    What is the main function of pancreatic lipase in lipid digestion?

    <p>To hydrolyze triglycerides into free fatty acids and monoglycerides</p> Signup and view all the answers

    How are free fatty acids absorbed by enterocytes in the small intestine?

    <p>Simple diffusion and facilitated diffusion</p> Signup and view all the answers

    Where are chylomicrons formed in the body?

    <p>Enterocytes of the intestinal lining</p> Signup and view all the answers

    What is the primary function of enterocytes in the context of lipid digestion and absorption?

    <p>Absorption and re-esterification of fatty acids and monoglycerides</p> Signup and view all the answers

    After lipid digestion and absorption, dietary fats are principally absorbed as:

    <p>2-monoacylglycerol and free fatty acids</p> Signup and view all the answers

    Which of the following components is incorporated into chylomicrons in the Golgi apparatus?

    <p>All of the above</p> Signup and view all the answers

    Chylomicrons primarily consist of: A) 50% cholesterol and 50% triglycerides, B) 90% triglycerides and 10% cholesterol esters, C) 90% triglycerides, apolipoproteins, and phospholipids, D) 10% triglycerides, 40% cholesterol, and 50% proteins.

    <p>90% triglycerides, apolipoproteins, and phospholipids</p> Signup and view all the answers

    What is the primary function of Apo C in chylomicrons?

    <p>To facilitate the uptake of chylomicrons into tissues</p> Signup and view all the answers

    Which of the following statements is true regarding LPL (lipoprotein lipase) in adipocytes?

    <p>LPL expression is upregulated by insulin.</p> Signup and view all the answers

    In the fed state, triglycerides (TGs) are primarily taken up by which of the following? (Select one)

    <p>Adipocytes</p> Signup and view all the answers

    In the fasting state, triglycerides are preferentially taken up by which of the following cells?

    <p>Muscle cells</p> Signup and view all the answers

    Glucose is metabolized by glycolysis to produce:

    <p>Acetyl CoA</p> Signup and view all the answers

    Acetyl CoA is diverted from the TCA cycle into lipogenesis, which is catalyzed by which of the following enzymes?

    <p>Fatty Acid Synthase</p> Signup and view all the answers

    Triglycerides are packaged into which type of lipoproteins for secretion into the blood?

    <p>VLDL</p> Signup and view all the answers

    When the body needs more energy, it mobilizes triglycerides through the process of:

    <p>Lipolysis</p> Signup and view all the answers

    Which of the following statements is correct regarding β-oxidation?

    <p>It generates acetyl CoA from fatty acids.</p> Signup and view all the answers

    What is the primary product of lipolysis?

    <p>Glycerol and free fatty acids</p> Signup and view all the answers

    Which of the following statements about β-oxidation is true?

    <p>It converts fatty acids into acetyl CoA units.</p> Signup and view all the answers

    What is the main purpose of β-oxidation in metabolism?

    <p>To generate ATP from fatty acids.</p> Signup and view all the answers

    Which enzyme is involved in the rate-limiting step of lipolysis?

    <p>Hormone-sensitive lipase (HSL)</p> Signup and view all the answers

    What triggers the mobilization of fatty acids from adipose tissue?

    <p>Low glucose availability</p> Signup and view all the answers

    Which of the following is NOT a product of β-oxidation?

    <p>Glycerol</p> Signup and view all the answers

    Which enzyme is responsible for hydrolyzing triglycerides in circulating chylomicrons and VLDLs to free fatty acids in the fed state?

    <p>Lipoprotein lipase (LPL)</p> Signup and view all the answers

    What happens to the free fatty acids released by hormone-sensitive lipase (HSL) during fasting?

    <p>They bind to albumin and are transported to tissues for β-oxidation.</p> Signup and view all the answers

    Which enzyme is upregulated by insulin in the fed state to promote the storage of triglycerides?

    <p>Lipoprotein lipase (LPL)</p> Signup and view all the answers

    What is the effect of catecholamines on hormone-sensitive lipase (HSL)?

    <p>Promotion of HSL phosphorylation</p> Signup and view all the answers

    Which signaling pathway is activated by glucagon and catecholamines to promote lipolysis?

    <p>cAMP/PKA pathway</p> Signup and view all the answers

    How does insulin inhibit lipolysis at the molecular level?

    <p>By activating tyrosine kinase receptors and preventing HSL phosphorylation</p> Signup and view all the answers

    Which of the following hormones enhances the effects of catecholamines and glucagon on lipolysis?

    <p>Glucocorticoids</p> Signup and view all the answers

    Which hormone is primarily responsible for increasing cAMP levels in the fasted state?

    <p>Glucagon</p> Signup and view all the answers

    Which hormone directly promotes lipolysis through activation of protein kinase A (PKA)?

    <p>Glucagon</p> Signup and view all the answers

    Which enzyme is activated by PKA to initiate lipolysis in adipocytes?

    <p>Hormone-sensitive lipase (HSL)</p> Signup and view all the answers

    Which of the following is required for the transport of long-chain fatty acids into the mitochondrial matrix?

    <p>Acyl-carnitine translocase</p> Signup and view all the answers

    Which enzyme is responsible for replacing CoA with carnitine on a fatty acid during its transport into the mitochondria?

    <p>Carnitine Palmitoyl Transferase I (CPT I)</p> Signup and view all the answers

    Which of the following enzymes initiates the β-oxidation of fatty acids in the mitochondrial matrix?

    <p>Acyl-CoA dehydrogenase</p> Signup and view all the answers

    Which enzyme activates fatty acids to acyl-CoA for β-oxidation?

    <p>Acyl-CoA synthase (thiokinase)</p> Signup and view all the answers

    What is the significance of carnitine in the transport of fatty acids into the mitochondria?

    <p>It facilitates the transport of long-chain fatty acids across the mitochondrial membrane.</p> Signup and view all the answers

    Which of the following molecules inhibits Carnitine Palmitoyl Transferase I (CPT I), thereby preventing the entry of fatty acids into the mitochondria for $\beta$-oxidation?

    <p>Malonyl-CoA</p> Signup and view all the answers

    What is the primary effect of insulin on hormone-sensitive lipase (HSL) activity in adipose tissue?

    <p>Inhibits HSL phosphorylation, decreasing lipolysis</p> Signup and view all the answers

    Which of the following hormones promotes the breakdown of triglycerides in adipose tissue by stimulating hormone-sensitive lipase (HSL)?

    <p>Catecholamines</p> Signup and view all the answers

    The regulation of β-oxidation by levels of free fatty acids is largely dependent on which of the following factors?

    <p>Insulin and glucagon levels</p> Signup and view all the answers

    Which of the following correctly explains how β-oxidation and fatty acid synthesis are kept separate in the cell?

    <p>Malonyl-CoA inhibits β-oxidation while promoting fatty acid biosynthesis.</p> Signup and view all the answers

    Which of the following best describes how hormone-sensitive lipase (HSL) is regulated during fasting?

    <p>HSL is phosphorylated and activated by catecholamines and glucagon.</p> Signup and view all the answers

    Which of the following best describes the relationship between free fatty acid (FFA) metabolism and hormone-sensitive lipase (HSL)?

    <p>HSL increases free fatty acid release from adipose tissue, especially when stimulated by glucagon and catecholamines.</p> Signup and view all the answers

    Which of the following is NOT a ketone body?

    <p>Oxaloacetate</p> Signup and view all the answers

    Which of the following conditions leads to the formation of ketone bodies?

    <p>Depleted glycogen stores and low glucose availability</p> Signup and view all the answers

    Which of the following symptoms is most closely associated with diabetic ketoacidosis?

    <p>Dehydration, confusion, and abdominal pain</p> Signup and view all the answers

    What is the main function of brown adipose tissue (BAT)?

    <p>To generate heat in response to cold temperatures</p> Signup and view all the answers

    Which of the following molecules is primarily responsible for the uncoupling of oxidative phosphorylation in brown adipose tissue?

    <p>Uncoupling Protein 1 (UCP1)</p> Signup and view all the answers

    What is the primary defect in Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD)?

    <p>Impaired breakdown of medium-chain fatty acids</p> Signup and view all the answers

    Which of the following is a common clinical sign of MCADD?

    <p>Intolerance to prolonged fasting</p> Signup and view all the answers

    What is the primary reason for hypoglycemia in patients with MCADD? A) Excessive glucose production B) Impaired gluconeogenesis C) Inability to metabolize medium-chain fatty acids D) Increased insulin sensitivity

    <p>Inability to metabolize medium-chain fatty acids</p> Signup and view all the answers

    How does Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) affect ketogenesis?

    <p>It impairs ketogenesis</p> Signup and view all the answers

    Which enzyme is deficient in Medium Chain Acyl-CoA Dehydrogenase Deficiency?

    <p>Medium Chain Acyl-CoA Dehydrogenase</p> Signup and view all the answers

    Study Notes

    Dietary Fats Overview

    • Major dietary fats include saturated fats (found in meat, butter, cheese, chocolate), transfats (found in meat and dairy), and unsaturated fats (derived from oils, fish, plants, avocados, nuts).
    • Most dietary fats exist as triglycerides, consisting of three fatty acids attached to a glycerol backbone.
    • Functions of dietary fats encompass energy reserves, temperature regulation, organ protection, and absorption of fat-soluble vitamins.
    • Digestion occurs primarily in the small intestine through lipase enzymes.

    Functions of Fatty Acids

    • Facilitate absorption and transport of nutrients.
    • Serve as nutrient-rich energy storage in adipose tissue through triglyceride synthesis.
    • In fasting, fatty acids are mobilised through lipolysis for energy usage.
    • Liver needs in ketogenesis engage fatty acids for energy production.

    Lipid Transport and Metabolism

    • Lipids are transported as triglycerides, which are hydrophobic and require lipoproteins for transport in aqueous environments.
    • Lipoproteins consist of a triglyceride and cholesterol core enveloped in phospholipids.
    • Chylomicrons, formed post-digestion, transport dietary fats and fat-soluble vitamins from the intestine into the bloodstream.

    Chylomicron Formation and Function

    • Chylomicrons comprise phospholipids, apolipoproteins (ApoB, ApoC, ApoE), triglycerides, cholesterol esters, and fat-soluble vitamins.
    • After their synthesis, chylomicrons enter the lymphatic system and the bloodstream via the thoracic duct.
    • Lipoprotein lipase (LPL) hydrolyzes triglycerides, facilitating absorption into adipocytes or muscle cells based on the metabolic state.

    Triglyceride Synthesis and Lipolysis

    • Triglycerides are predominantly taken from chylomicrons for storage in adipose tissue, particularly following meals.
    • In fasting, adipocytes release free fatty acids into circulation using lipases, including hormone-sensitive lipase (HSL).
    • Hormonal activity regulates lipolysis with insulin inhibiting and catecholamines stimulating fat breakdown.

    Energy Extraction from Fatty Acids

    • β-oxidation is the primary method for extracting energy from fatty acids, occurring in the mitochondria through three stages: activation, transport into mitochondria, and actual β-oxidation.
    • Involves breaking down fatty acids into acetyl-CoA for energy generation via the TCA cycle and electron transport chain.

    Ketone Bodies and Ketogenesis

    • Ketogenesis occurs in the liver when glucose is scarce, resulting in the formation of acetoacetate, β-hydroxybutyric acid, and acetone from acetyl-CoA.
    • Ketone bodies serve as an alternative energy source for tissues, especially the brain, during prolonged fasting or diabetes.
    • High levels of ketone bodies can lead to ketoacidosis, with symptoms like nausea, dehydration, and confusion.

    Brown Adipose Tissue (BAT)

    • Different from white adipose tissue, BAT primarily generates heat (thermogenesis) in response to cold, particularly in newborns and hibernating mammals.
    • Characterized by multiple lipid droplets, iron-containing mitochondria, and uncoupling protein 1 (UCP1), which promotes heat generation instead of ATP production.

    Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD)

    • A genetic disorder impacting the breakdown of medium-chain fatty acids, resulting in severe clinical implications like hypoglycaemia and acidosis due to fatty acid accumulation.
    • Treatment consists of dietary management to prevent fasting and ensuring glucose supplementation.

    Fed State (High Levels of Insulin)

    • Dietary triglycerides are transported as chylomicrons to adipose tissue.
    • Chylomicrons interact with Lipoprotein Lipase (LPL) through Apolipoprotein C (ApoC) on their surface.
    • LPL hydrolyzes triglycerides into monoacylglycerol and free fatty acids (FAs).
    • Free fatty acids diffuse into adipocytes for uptake.
    • Inside adipocytes, fatty acids are re-esterified into triglycerides.
    • Triglycerides are stored in fat droplets within adipocytes, acting as energy reserves.
    • This energy storage process prepares the body for future energy needs.

    Fasting State/Exercise (Low Insulin, High Glucagon/Catecholamines)

    • Low insulin and high levels of glucagon or catecholamines activate lipolysis.
    • Hormone-Sensitive Lipase (HSL) and other lipases are phosphorylated and activated.
    • Stored triglycerides in adipose tissue are metabolized into free fatty acids and glycerol.
    • Free fatty acids bind to albumin for transport in the bloodstream to target tissues, including muscles.
    • Glycerol is transported to the liver for further metabolism, contributing to glycolysis or gluconeogenesis.

    Extraction of Energy from Fatty Acids

    • Energy is extracted from fatty acids through β-oxidation, occurring in the mitochondria.

    β-Oxidation Overview

    • Fatty acids are activated to fatty acyl-CoA by Acyl-CoA Synthetase before β-oxidation.
    • Fatty acyl-CoA is moved into the mitochondria via the carnitine shuttle, utilizing Carnitine Palmitoyl Transferase I (CPT I) and CPT II.
    • The β-oxidation cycle involves several critical enzymes:
      • Acyl-CoA Dehydrogenase: Converts acyl-CoA to enoyl-CoA.
      • Enoyl-CoA Hydratase: Hydrates enoyl-CoA to form hydroxyacyl-CoA.
      • 3-Hydroxyacyl-CoA Dehydrogenase: Converts hydroxyacyl-CoA to ketoacyl-CoA.
      • Beta-Ketothiolase: Cleaves ketoacyl-CoA to release Acetyl-CoA and a shorter acyl-CoA.
    • Each β-oxidation cycle shortens the fatty acid chain by two carbons, generating Acetyl-CoA, which enters the Krebs cycle for further energy production.

    Lipoproteins Overview

    • Lipoproteins are classified by size, lipid composition, and apolipoproteins; as triglycerides (TGs) are removed, size decreases and density increases.
    • Major apolipoproteins include Apo B, Apo C, and Apo E, vital for lipoprotein metabolism.

    Post-Absorption Transport of Triglycerides

    • Fat is absorbed mainly as 2-monoacylglycerol and free fatty acids (FAs).
    • Resynthesis of triglycerides occurs in the endoplasmic reticulum, incorporating into chylomicrons in the Golgi apparatus.
    • Chylomicrons consist of phospholipids, triglycerides (90%), cholesterol esters, fat-soluble vitamins, and apolipoproteins (ApoB, ApoC, ApoE).
    • Chylomicrons enter lymphatic circulation and then the bloodstream via the thoracic duct.

    Lipoprotein Lipase & Lipogenesis

    • Chylomicrons interact with lipoprotein lipase (LPL), primarily synthesized in adipose, muscle, and heart tissues; not present in liver or brain.
    • In the fed state, triglycerides are taken up by adipocytes for storage, while in fasting, muscle cells utilize triglycerides for energy.
    • LPL hydrolyzes TGs into free fatty acids and monoacylglycerol for reassembly into triglycerides in adipocytes, regulated by insulin.

    Triglyceride Synthesis

    • After meals, FAs used for synthesis mainly derive from chylomicrons.
    • Excess glucose from carbohydrate-rich meals is converted to acetyl CoA, diverted into lipogenesis, and catalyzed by Fatty Acid Synthase.
    • Synthesized triglycerides are packaged into very-low-density lipoproteins (VLDLs) for secretion into the bloodstream.

    Lipolysis

    • Lipolysis refers to the breakdown of triglycerides into glycerol and free fatty acids, primarily during fasting or exercise.
    • Involves three key enzymes: Adipose Triglyceride Lipase (ATGL), Hormone Sensitive Lipase (HSL), and Monoacylglycerol Lipase (MGL).
    • Free fatty acids circulate bound to albumin; glycerol is sent to the liver for further metabolism.

    Hormonal Regulation of Lipolysis

    • HSL activity is modulated by phosphorylation; it is active when phosphorylated via Protein Kinase A.
    • Insulin inhibits lipolysis by preventing HSL phosphorylation, while glucagon and catecholamines promote lipolysis by activating HSL.

    Energy Extraction from Fatty Acids (β-Oxidation)

    • β-oxidation is the metabolic pathway via which fatty acids are broken down for energy, occurring primarily in mitochondria.
    • The process consists of three stages: activation of fatty acids, transport into mitochondria via the carnitine shuttle, and β-oxidation in the mitochondrial matrix.
    • β-Oxidation entails removing 2-carbon units from fatty acids, producing Acetyl-CoA for the TCA cycle.

    Ketone Bodies

    • Ketone bodies (acetoacetate, β-hydroxybutyric acid, acetone) serve as an alternative energy source during glucose scarcity.
    • Synthesized in the liver from acetyl CoA during fasting or diabetes when oxaloacetate is depleted.

    Brown Adipose Tissue Functionality

    • Brown adipose tissue (BAT) generates heat (thermogenesis) through uncoupling oxidative phosphorylation via uncoupling protein 1 (UCP1), important for thermoregulation.
    • BAT is richly vascularized, contains multiple lipid droplets, and is packed with iron-containing mitochondria.

    Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD)

    • MCADD impairs β-oxidation of medium-chain fatty acids due to genetic defects, leading to hypoglycemia and acidosis from fatty acid accumulation.
    • Preventive treatment involves avoiding fasting and ensuring glucose supplementation.

    Dietary Fats

    • Dietary sources include saturated fats (meat, butter), trans fats (meat and dairy), and unsaturated fats (oils, avocados, nuts).
    • Triglycerides, the main storage form of energy, yield significantly more energy per gram than carbohydrates.

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    Description

    This quiz covers the major types of dietary fats including saturated, trans, and unsaturated fats. It discusses their sources, chemical structure, and functions in the body such as energy reserve and nutrient absorption. Test your knowledge about how dietary fats impact health and nutrition.

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