Q&n y

• Why are lipids indispensable for their structure and function?

  Due to their hydrophobic and nonpolar nature.
• What are the most abundant lipids in our body?

  Triacylglycerols, comprising 85-90% of body lipids.
• Why should fat be the fuel reserve of the body?

  Because triacylglycerols yield 9 Cal/g and are non-polar and hydrophobic.
• In which form can lipids be transported?

  In the form of lipoprotein.
• What are the types of lipoproteins and their functions?

  1. Chylomicrons: Transport dietary triacylglycerol.
  2. Very low density lipoproteins (VLDL): Transport endogenously synthesized triacylglycerols.
  3. Low density lipoproteins (LDL): Transport cholesterol from liver to body.
  4. High density lipoproteins (HDL): Transport cholesterol from body to liver.
• Which enzyme participates in the degradation of TAG in adipose tissue?

  Hormone sensitive triacylglycerol lipase.
• What are the regulatory hormones in hormone sensitive lipase (HSL)?

  Epinephrine, norepinephrine, glucagon, thyroxine, ACTH.
• Where does the metabolism of fatty acids occur?

  In the liver.
• What is the difference between activation and oxidation of fatty acids?

  Activation occurs in the cytosol, while oxidation occurs in mitochondria.
• Define beta oxidation.

  β-Oxidation is the oxidation of fatty acids on the β-carbon atom.
• What is the role of carnitine in fatty acid oxidation?

  Carnitine is transported across the membrane to mitochondria.
• What is the regulatory enzyme of beta oxidation of fatty acids?

  Carnitine acyltransferase I.
• Define ketogenesis.


  Ketogenesis is the synthesis of ketone bodies.
• Where does ketogenesis occur according to the organ and cell?

  In the liver mitochondria.
• What are the general functions of lipids?

  • Excellent energy reserves
  • Structure of cell membranes
  • Essential fatty acids (EFA)
  • Hormone synthesis
• What are the causes of lipid disorder?

  Shortage and overtaking in lipid intake.
• What are the functions of cholesterol?

  Serves as a building block for synthesizing steroid hormones, vitamin D, and bile acids.
• How can we prevent lipid disorder?

  • Reduce fat intake
  • Drink at least 8 glasses of water daily
  • Increase intake of vegetables, fruits, and whole grains
• What is the difference between lipolysis and lipogenesis?

  Lipolysis is the degradation of triacylglycerol, while lipogenesis is the formation of fat.
• What is the function of glycerol?

  Glycerol serves as a backbone for triglycerides.
• What is the advantage of fatty acid production?

  For energy production during long starvation.
• What are the organs that do not use fatty acids as energy?

  The brain and erythrocytes.
• What is the difference between Acyl transferase 1 and 2?

  Acyl transferase 1 transfers acyl group of acyl CoA to carnitine, while Acyl transferase 2 converts acyl-carnitine to acyl CoA.
• What is the meaning of ketonuria?

  Ketonuria is the excretion of ketone bodies in urine.
• Which hormones participate in the regulation of ketogenesis?

  Glucagon stimulates ketogenesis, while insulin inhibits it.
• What are the stages of fatty acid synthesis?

  1. Production of acetyl CoA and NADPH
  2. Conversion of acetyl CoA to malonyl CoA
  3. Reactions of fatty acid synthase complex
• Can we get cholesterol from plant products? Why or why not?

  No, because cholesterol is made in the liver and plants do not have a liver.
• Which lipoprotein cannot be separated by electrophoresis?

  Free fatty acid albumin.
• What are the stages of fatty acid oxidation?

  1. Activation of fatty acids in the cytosol
  2. Transport of fatty acids into mitochondria
  3. β-Oxidation proper in the mitochondrial matrix
• Explain fatty acid activation.

  Fatty acids are activated to acyl CoA by thiokinases or acyl CoA synthetases, requiring ATP, coenzyme A, and Mg$^{2+}$.
• How many steps consist of the transport of Acyl CoA into mitochondria?

  In 4 steps.
• How many compounds do ketone bodies consist of?

  3 compounds: acetone, acetoacetate, and β-hydroxybutyrate.
• What are the precursors for ketone bodies?

  Acetyl CoA.
• What are the stages of ketone bodies synthesis?

  1. Two moles of acetyl CoA condense to form acetoacetyl CoA.
  2. Acetoacetyl CoA combines with another acetyl CoA to produce HMG CoA.
  3. HMG CoA lyase cleaves HMG CoA to produce acetoacetate and acetyl CoA.
  4. Acetoacetate can undergo spontaneous decarboxylation to form acetone.
  5. Acetoacetate can be reduced to β-hydroxybutyrate.
• What is the use of ketone bodies?

  As an alternative source of energy.
• What tissues mostly use ketone bodies as energy?

  Skeletal muscle, cardiac muscle, and renal cortex.
• When does the production of ketone bodies and their utilization become more significant?

  When glucose is in short supply, as observed in starvation and diabetes mellitus.
• What happens during the overproduction of ketone bodies?

  When synthesis exceeds utilization, their concentration in blood increases, known as ketonemia.
• What is the meaning of ketonemia?


  Increase of ketone bodies in the circulating blood.
• Define ketosis.


  Ketosis is commonly associated with starvation and severe uncontrolled diabetes mellitus.