Biochemistry of Lipids 1

Biochemistry of Lipids

Understand the structure, function and classification of lipids

Structure

  • Lipids are organic, water-insoluble macromolecules that are soluble in non-polar solvents (ether, ethanol)
  • Composed of fatty acid monomers
  • Have a long, non-polar hydrocarbon chain with a small polar region containing oxygen

Function

  • Storage form of energy- 2.25x that of carbohydrates
  • Structural components
  • Insulation
  • Cushioning effect

Discuss the chemistry and importance of different types of lipids

Simple lipids

  • Esters of fatty acids with alcohols
  • Fats: esters of fatty acids with glycerols
  • Insoluble in water; soluble in ether, chloroform, benzene
  • Good solvents for other fats, fatty acids, fat soluble vitamins
  • Food reserve
  • Insulation
  • Cushioning effect

Waxes

  • Esters of fatty acids with higher molecular weight alcohols
  • Waxy coating on fruits and leaves protect from predators and desiccation
  • Waxy coating on animal fur and feathers serve as water repellents

Complex lipids

  • Esters of fatty acids with alcohol containing other groups
  • Phospholipids
    • Esters of fatty acids with glycerol containing an esterified phosphoric acid and a nitrogen base
    • Nerve tissue
    • Liver
    • Kidney
    • Pancreas
    • Heart
    • Carriers for inorganic ions across the membranes
    • Blood clotting
    • Form the structures of membranes, matrix of cell wall, myelin sheath, microsomes and mitochondria.
  • Glycolipids
    • Amino alcohol (sphingosine) attached with an amine linkage to a fatty acid; glycosidically bonded to a carbohydrate
    • Cerebrosides
      • Main constituent of myelin sheaths
      • Nerve impulse conduction and signal transduction
    • Gangliosides
      • Found in the brain
      • Specific receptors for pituitary hormones
      • Cell-cell recognition, growth and differentiation of tissues

Derived lipids

  • Compounds during the hydrolysis of simple and complex lipids
    • Fatty acids
    • Glycerol
    • Steroids
    • Lipid soluble vitamins
    • Steroid hormones

Understand the biological significance of different fatty acids

  • Fatty acids are straight aliphatic chains with a methyl group at one end and a carboxyl group at the other end.
  • The hydrocarbon chain is hydrophobic; the carboxylate group is hydrophilic.
  • Occur primarily as esters of glycerol
  • Short FA: 2-4 C
  • Medium FA: 6-10 C
  • Long FA: 12-26+ C
  • Saturated FA: no double bond
  • Unsaturated FA: one or more double bond
  • Can exhibit either cis or trans isomerism due to double bond
    • Cis is most naturally occurring and causes the chain to bend.

Trans fatty acids

  • Detrimental to health
  • Hydrogenation of vegetable oils
  • Ruminant fat contains trans due to isomerization of plant cis via rumen microbes.
  • Compete with essential fatty acids which can increase deficiency
  • Increase cholesterol level and the formation of atherosclerosis

Function

  • Constituents of phospholipids and glycolipids
  • Fuel molecules (as triglycerides)
  • Physical protection for organs

Essential fatty acids

  • Polyunsaturated fatty acids that cannot be synthesized
    • Linoleic acid (omega 6)
      • Almonds, eggs
    • Linolenic acid (omega 3)
      • Oily fish
    • Arachadonic acid in felines (others can form from linoleic acid)
  • Deficiency
    • Scaly dermatitis
    • Decreased availability of precursors for eicosanoid synthesis
    • Affects fluidity of membrane structure

Explain phospholipids and know its different types and significance

  • Phospholipids
    • Esters of fatty acids with glycerol containing an esterified phosphoric acid and a nitrogen base

Name

Significance

Phosphatidylcholine (lecithin)

Prevents accumulation of lipids in tissues.

Phosphatidylethanolamine (cephalin)

In nervous tissue.

Role in membrane fusion during cytokinesis.

Role in secretion of lipoproteins in the liver.

Phosphatidylinositol

Precursor for some second messengers

Phosphatidylserine

Brain function

Lysophospholipids

Lysis of cell membrane

Plasmalogens

10% of PL in brain and muscle

Platelet activating factor

Cardiolipin

Needed for maintenance of ETC

Sphingomyelins

Constituent of myelin of nerve fibers

Understand lipoproteins and their different types

  • Lipoprotein complex is composed of
    • 45% triacylglycerol
    • 35% phospholipids
    • 15% cholesterol and cholesterol esters
    • 5% free fatty acids
    • Protein
  • Density of lipoproteins increases as the protein content rises and the lipid content falls
  • Chylomicrons
    • Predominant- triacylglycerol (50%) and cholesterol (23%)
  • Very low density lipoproteins (VLDL)
    • Predominant- triacylglycerol (50%) and cholesterol (23%)
  • Low density lipoproteins (LDL)
    • Predominant- cholesterol (46%) and phospholipids (23%)
  • High density lipoproteins (HDL)
    • Predominant- phospholipid (27%) and proteins (45%)

Importance

  • Transport and deliver lipids to tissues
  • Maintains structural integrity of cell surface, mitochondria, microsomes
  • Diagnostic
    • VLDL and LDL increase in severe diabetes mellitus, atherosclerosis etc.