Untitled Quiz

Lipids

• Organic compounds insoluble in water (hydrophobic)
• Contain carbon, hydrogen, and oxygen, but less oxygen than carbohydrates
• Functions:
  • Mechanical protection
  • Thermal insulation (under the skin)
  • Electrical insulation (around nerves)
  • Cell membrane structure
  • Steroid hormones
  • Energy storage

Fatty Acids

• Monocarboxylic acids (R-COOH) with:
  • Hydrocarbon chain (R): hydrophobic
  • Carboxyl group (–COOH): ionizes to –COO- (hydrophilic)
• Amphipathic molecules (have both hydrophilic & hydrophobic regions)
• Long-chain fatty acids are highly water-insoluble
• Fatty acids are transported in the blood with a protein (albumin).
• Usually contain an even number of carbon atoms.

Types of Fatty Acids

• Saturated Fatty Acids: No double bonds

  • Butyric acid (4C): CH3 - CH2 - CH2 - COOH (4:0)
  • Palmitic acid (16 C): CH3 - (CH2)14 – COOH (16:0)
  • Stearic acid (18C): CH3 - (CH2)16 - COOH (18:0)

• Unsaturated Fatty Acids: One or more double bonds

  • Oleic acid (18C): One double bond between C9 & C10.
  • Linoleic acid (18 C): Two double bonds between C9 & C10 and C12 & C13.
  • Linolenic acid (18 C): Three double bonds between C9-10, C12-13 & C15-16.

Essential Fatty Acids (PUFA)

• Cannot be synthesized in the human body
• Must be supplied with food
• Two essential fatty acids in humans:
  • Linoleic acid (w6): Precursor of arachidonic acid, important for prostaglandin synthesis.
  • α-Linolenic acid (w3): Precursor for other w3 (omega-3) fatty acids, important for growth, development, and protection from heart problems.

Simple Lipids

• Natural fats or Triacylglycerols (TAG): Esters of 3 fatty acids with the tri-hydroxy alcohol glycerol
• Fats: Solid at room temperature.
• Oils: Liquid at room temperature.
• Occurrence of neutral fat:
  • Found in plants: cottonseed oil, olive oil, palm oil, coconut oil, etc.
  • Found in animals: butter.
  • Found in marine oils: cod liver oil.

Conjugated Lipids

• Phospholipids (PL):

  • Important for cell membrane structure
  • Helps triglyceride absorption in the small intestine
  • Lecithin acts as a lipotropic factor
  • Lecithin is a component of lung surfactant
  • Cardiolipin is used to detect syphilis
  • Sphingophospholipids act as electrical insulators (myelin sheath).

• Glycolipids: Lipids linked to carbohydrates.

• Plasma Lipoproteins: Spherical macromolecular complexes of lipids and proteins (apoproteins, apolipoproteins)

  • Function: Transport lipids in plasma
  • Types:
    • Chylomicrons: Lowest density & largest size, highest % of lipid & the lowest % of protein.
    • VLDLs & LDLs: Denser, with higher ratios of protein to lipid than chylomicrons.
    • HDL: The densest, containing the highest level of protein to lipid.

Functions of Plasma Lipoproteins

• Chylomicrons: Carry exogenous dietary lipids (mainly TG) from the intestine to peripheral tissues.
• VLDLs: Carry endogenous lipid (mainly TG) from the liver to extrahepatic tissues.
• LDLs: Transfer cholesterol from blood to tissues (originate from VLDLs in blood).
• HDLs: Take cholesterol from peripheral tissues and transfer it to the liver.