lipid metabolism

• What are triacylglycerols also known as?

  Triglycerides
• What is the most abundant type of lipid in the human body?

  Triacylglycerols (TAG)
• How are triacylglycerols formed?

  By esterification of 3 fatty acids to 1 glycerol
• Where are triacylglycerols located in the body?

  Within fat cells (adipocytes)
• What distinguishes simple TAGs from mixed TAGs?

  Simple TAGs have identical fatty acids
• What are lipoproteins?

  Conjugated proteins that transport lipids
• What is the structure of lipoproteins?

  Spherical lipid core with a phospholipid shell
• What do chylomicrons transport?

  Dietary triacylglycerols (TAG)
• What do Very-Low-Density Lipoproteins (VLDL) transport?

  Endogenous TAG from liver to adipose tissue
• What do Low-Density Lipoproteins (LDL) transport?

  Endogenous cholesterol from liver to tissue
• What do High-Density Lipoproteins (HDL) do?

  Collect excess cholesterol from tissues
• What is the process of TAG storage and mobilization?

  • Storage in adipocytes
  • TAGs form droplets, merge into fat globule
  • Mobilization through hydrolysis to free fatty acids
  • Influenced by epinephrine and glucagon
  • Requires hormone-sensitive lipase
• What happens to glycerol during TAG hydrolysis?

  It is released into the bloodstream
• What is glycerol converted into in the liver or kidneys?

  DHAP (Dihydroxyacetone phosphate)
• What enzyme phosphorylates glycerol to glycerol-3P?

  Glycerol kinase
• What is the first step in fatty acid activation?

  Conversion into a high-energy derivative of Coenzyme A
• How many high-energy phosphate bonds are expended during fatty acid activation?

  2 high-energy phosphate bonds
• What is the role of carnitine in fatty acid transport?

  It shuttles Acyl CoA into the mitochondrial matrix
• What enzyme transfers the acyl group to carnitine?

  Carnitine palmitoyl transferase I
• What happens to the fatty acyl group after it enters the mitochondrial matrix?

  It is transferred back to CoA
• Where does fatty acid β-oxidation occur?

  Mitochondrial matrix
• What is the carrier for intermediates during β-oxidation?

  Coenzyme A
• What are the oxidizing agents used in β-oxidation?

  FAD and NAD
• What are the steps of fatty acid β-oxidation?

  1. Oxidation (dehydrogenation)

  • Enzyme: Acyl CoA dehydrogenase
  • Requires: FAD

  1. Hydration

  • Enzyme: Enoyl CoA hydratase
  • Requires: H2O

  1. Oxidation (dehydrogenation)

  • Enzyme: β-Hydroxyacyl CoA dehydrogenase
  • Requires: NAD

  1. Thiolysis

  • Enzyme: Thiolase
  • Requires: CoA-SH
• What does each turn of the β-oxidation sequence produce?

  1 FADH2, 1 NADH, 1 Acetyl CoA
• How many repetitions are required to oxidize one molecule of stearic acid?

  8 repetitions
• What are the products produced by 8 repetitions of β-oxidation of stearic acid?

  8 FADH2, 8 NADH, 9 Acetyl CoA
• What is the energy required to activate a fatty acid before oxidation?

  2 ATP
• What is the net ATP production from the oxidation of stearic acid?

  120 ATP
• What additional enzymes are required for the oxidation of unsaturated fatty acids?

  Cis-trans isomerase and epimerase
• What is the fate of Acetyl CoA generated from fatty acid oxidation?

  Processed for ATP or converted to ketone bodies
• What are the energy utilizations of various organs?

  • Skeletal muscle: Glucose (active), Fatty acids (resting)
  • Cardiac muscle: Fatty acids, Ketone bodies, Glucose, Lactate
  • Liver: Fatty acids
  • Brain: Glucose, Ketone bodies (fatty acids cannot cross BBB)
• What must be present for Acetyl CoA to enter the Krebs Cycle?

  Adequate amounts of oxaloacetate
• What upsets the balance required for Acetyl CoA to enter the Krebs Cycle?

  High fat intake, diabetic conditions, prolonged fasting
• What is ketogenesis?

  Formation of ketone bodies in the liver
• What are the steps of ketogenesis?

  1. Condensation (Enzyme: Thiolase)
  2. Condensation (Enzyme: HMG CoA Synthase)
  3. Chain Cleavage (Enzyme: HMG CoA lyase)
  4. Hydrogenation (Enzyme: β-hydroxybutyrate dehydrogenase)
• What is the normal concentration of ketone bodies in the blood?

  Very low (1 mg/100 mL)
• What is Ketonemia?

  Excess ketone bodies in the blood
• What is Ketonuria?

  Ketones appear in the urine
• What is ketosis?

  High levels of ketone bodies in blood and urine