Triglycerides & Fatty Acids

• Lipids


  Broad term encompassing fats, oils, waxes and other hydrophobic molecules such as cholesterol
• Fat


  Solid at room temperature
• Oil


  Liquid at room temperature
• Fatty foods are rich in Triglycerides (TG)
• Triglycerides (TG) or Triacylglycerols (TAG)


  Three fatty acid chains are ester-linked to glycerol backbone
• Triglycerides (TG)


  • O-C-CH2-O-CH2-O-CH2-O

  Glycerol backbone with 3 fatty acid chains ester-linked
• Fatty acids

  Long-chain (12-24C) hydrocarbons (acyl)
• Types of fatty acids

  • Saturated - no double bonds
  • Monounsaturated - one double bond
  • Polyunsaturated - more than 1 double bonds
• Cis and trans fatty acids

  Cis - double bonds on same side

  Trans - double bonds on opposite sides
• Omega or n system for naming fatty acids

  Systematic name based on number of carbons and double bonds

  Common name based on position of first double bond from methyl end
• Oleic acid is an omega 9 fatty acid
• Alpha-Linolenic acid


  An omega 3 fatty acid
• Linoleic acid


  An omega 6 fatty acid
• Essential fatty acids (EFA)

  • Humans don't have the right desaturase to add double bonds lower than omega 9, so omega 3 or omega 6 FA have to come from the diet
• Fatty acid length


  Affects bilayer thickness
• Degree of unsaturation


  Affects membrane fluidity
• Brain is ~60% lipid, enriched in omega 3 and 6 fatty acids
• Some fatty acids are precursors to signalling molecules like prostaglandins, leukotrienes, thromboxanes
• Digestion of dietary fats/oils (lipids)


  Majority of lipid in food is triglycerides

  Digested by pancreatic lipases

  Hydrolysis of ester bonds

  Produces 2 monoacylglycerol and free fatty acids
• Absorption/assimilation of fatty acids


  Digested triglycerides are re-esterified in gut mucosa

  Fatty acids have to be activated using Coenzyme A first

  Triglycerides are packaged into lipoproteins for transport in blood to tissues
• Chylomicrons

  • Transport from gut to tissues
  • Mixture of lipid and protein
  • Phospholipid and cholesterol outer layer, triglyceride and cholesterol ester inner core
  • Contain apolipoproteins like ApoB48, ApoC2, ApoE
• Uptake of fatty acids into adipose tissue


  Lipoprotein lipase cleaves off fatty acids from chylomicrons which then enter cells

  When chylomicron has offloaded most TG it becomes a remnant and is removed by the liver
• Lipogenesis (synthesis of triglycerides) in adipose tissue


  Starting point is activated fatty acids and glycerol-3-phosphate

  Fatty acids are added one by one to glycerol-3-phosphate to form lysophosphatidic acid, phosphatidic acid, diacylglycerol, and finally triglycerides
• Glycerol-3-phosphate comes from DHAP in glycolysis
• What are fats like at room temperature (as triglyceride molecules)?

  Regular packing, more extensive intermolecular interactions
• What are oils like at room temperature (as triglyceride molecules)?

  Looser packing, fewer intermolecular interactions
• The fatty acid composition of triglycerides can be altered by enzymes called desaturases, which introduce double bonds into the hydrocarbon chain.
• Desaturation occurs at specific positions on the carbon skeleton, resulting in different types of unsaturated fats such as monounsaturates (one double bond) or polyunsaturates (multiple double bonds).
• Saturated fatty acids have no double bonds between carbons, while monounsaturated fatty acids have one double bond between carbons.
• What are triglycerides, and what is their basic structure?

  Triglycerides, also known as triacylglycerols (TAG), consist of three fatty acid chains ester-linked to a glycerol backbone. They are the main form of fat stored by the body and are a major component of human skin oils
• Define fatty acids and their types based on bond saturation

  Fatty acids are long-chain hydrocarbons with a carboxyl group at one end. They are categorized based on the presence of double bonds: saturated (no double bonds), monounsaturated (one double bond), and polyunsaturated (more than one double bond)
• How do the number of double bonds in fatty acids influence their physical properties?

  The number of double bonds affects the melting point of fatty acids. More double bonds lead to a lower melting point, contributing to oils being liquid at room temperature, while fewer double bonds lead to fats being solid
• What are omega fatty acids, and name an example of an omega-3 and omega-6 fatty acid?

  Omega fatty acids are types of polyunsaturated fatty acids distinguished by the position of the first double bond in relation to the methyl end of the fatty acid. Examples include alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid)
• Explain the significance of essential fatty acids

  Essential fatty acids, such as omega-3 and omega-6, cannot be synthesized by humans and must be obtained from the diet. They play critical roles in normal physiology, including cell membrane structure and function, and are precursors to important signaling molecules
• Describe the role of enzymes elongases and desaturases in fatty acid metabolism

  Elongases are enzymes that extend the carbon chain of fatty acids by two carbons, while desaturases introduce double bonds into fatty acids. These enzymes are critical for modifying dietary and synthesized fatty acids into forms needed for various physiological functions
• How are dietary triglycerides processed and absorbed in the human body?

  Dietary triglycerides are primarily digested by pancreatic lipases, which hydrolyze the ester bonds to release free fatty acids and monoglycerides. These are absorbed by intestinal cells, re-esterified, and then transported in the blood within lipoproteins
• What is the role of lipoprotein lipase in fatty acid metabolism?


  Lipoprotein lipase is an enzyme that cleaves fatty acids from triglycerides in lipoproteins. It is found on the endothelial cells of capillaries, especially in adipose tissue, and facilitates the uptake of fatty acids into cells for storage or energy
• What is the role of ATP citrate lyase in fatty acid synthesis?

  ATP citrate lyase splits citrate, which is transported out of the mitochondria, back into oxaloacetate and acetyl-CoA in the cytoplasm. This is a critical step in providing the acetyl-CoA necessary for fatty acid synthesis in the cytosol
• Explain the difference between cis and trans fatty acids

  Cis fatty acids have hydrogen atoms on the same side of the double bond, causing a bend or "kink" in the chain, which lowers melting points and is common in unsaturated fats from natural sources. Trans fatty acids have hydrogen atoms on opposite sides of the double bond, making the chain straighter, often found in partially hydrogenated oils, and associated with adverse health effects
• What is the function of acyl-CoA synthetase in fatty acid metabolism?

  Acyl-CoA synthetase activates free fatty acids by attaching coenzyme A (CoA), forming fatty acyl-CoA. This activation is necessary for fatty acids to enter into metabolic pathways, including beta-oxidation or triglyceride synthesis