Lipid 4

• What is the primary source of fatty acids for the body?

  Dietary intake
• How can carbohydrates and proteins be converted to fatty acids?

  They can be converted when in excess
• Where does fatty acid synthesis primarily occur in adult humans?

  Liver and lactating mammary glands
• What is the role of acetyl CoA in fatty acid synthesis?

  It provides carbons for the fatty acid chain
• What is lipogenesis?

  Synthesis of fatty acids from nonlipid precursors
• What are the key precursors and enzymes involved in fatty acid synthesis?

  • Acetyl CoA (Primer)
  • Malonyl CoA (Building unit)
  • ATP
  • NADPH
  • Bicarbonate (HCO3)
  • Fatty Acid Synthase
• What are the five steps of de novo fatty acid synthesis?

  1. Production of cytosolic acetyl CoA
  2. Carboxylation of acetyl CoA to malonyl CoA
  3. Action of fatty acid synthase
  4. Elongation of fatty acid chains
  5. Desaturation of fatty acid chains
• What is the first step in the production of cytosolic acetyl CoA?

  Condensation of acetyl CoA and OAA
• What promotes the translocation of acetyl CoA to the cytosol?

  High citrate concentration
• What enzyme hydrolyzes citrate to acetyl CoA and OAA?

  Citrate lyase
• What happens to OAA in the cytosol?

  It is dehydrogenated to malate
• What is the key enzyme for the carboxylation of acetyl CoA to malonyl CoA?

  Acetyl CoA Carboxylase (ACC)
• What is the rate-limiting step in fatty acid synthesis?

  Carboxylation of acetyl CoA to malonyl CoA
• How is ACC regulated in the short term?

  Allosteric inactivation by fatty acyl CoA
• What promotes the synthesis of ACC in the long term?

  Excess calories
• What are the steps involved in the action of fatty acid synthase?

  1. Acetyl binds to Cys-SH of KS
  2. Malonyl binds to PP-SH of ACP
  3. Forms Ketoacyl and releases CO2
  4. Forms 3-hydroxyl acyl using NADPH
  5. Releases H2O to form Enoyl
  6. Forms Acyl (4C)
  7. Transfers Acyl to Cys-SH for elongation
• What is the major source of NADPH for fatty acid synthesis?

  Pentose phosphate pathway
• How is fatty acid chain elongation achieved?

  By repeating the 7 steps in FA synthase
• What is the maximum length of fatty acids synthesized by the process?

  16C-palmitic acid or 18C-stearic acid
• What regulates the elongation of fatty acids?

  Availability of ATP and NADPH
• Where do desaturases operate in the cell?

  Smooth endoplasmic reticulum
• What is the typical position for double bond insertion in fatty acids?

  Between C9 and C10
• What factors regulate desaturase activity?

  Availability of O2 and hormones
• What are the mechanisms for regulating fatty acid synthesis?

  • Short term: Allosteric mechanisms and phosphorylation
  • Long term: Induction or repression of enzymes
• What promotes TAG synthesis in a well-fed state?

  Elevated levels of acetyl CoA and glycerol
• How are TAGs formed from acyl CoA?

  By esterification with glycerol 3 phosphate
• What are the types of phospholipids synthesized?

  • Plasmalogen
  • Phosphatidylcholine
  • Phosphatidyl ethanolamine
  • Phosphatidyl serine
  • Phosphatidyl inositol
  • Cardiolipin
• Which essential fatty acids cannot be synthesized by humans?

  Linoleic acid and alpha-linolenic acid
• What is a consequence of deficiency in essential fatty acids?

  Generalized scaly dermatitis
• How is arachidonic acid formed?

  From linoleic acid
• What are the steps involved in TAG lipolysis?

  1. TAG breakdown to free fatty acids (FFA)
  2. β-Oxidation of fatty acids
• What are the fates of glycerol in TAG lipolysis?

  • Converted to glycerol 3 phosphate
  • Used in glycolysis
• What is the role of glycerol in TAG synthesis?

  It is a backbone for TAG formation
• What is the process of converting glycerol to phosphatidylcholine?

  Through a series of transferase reactions
• What is the role of CDP in phosphatidylcholine synthesis?

  It acts as an intermediate in the pathway
• What is the significance of the acyl CoA in TAG synthesis?

  It provides fatty acids for TAG formation
• What is the final product of TAG synthesis?

  Triacylglycerol
• What is the role of kinases in TAG synthesis?

  They catalyze phosphorylation reactions
• What is the function of transferases in phospholipid synthesis?

  They transfer acyl groups in reactions
• What is the role of ethanolamine in phospholipid synthesis?

  It is a precursor for phosphatidylethanolamine