Organisation of Cellular Lipids and Membranes

Organisation of Cellular Lipids and Membranes

• Structural: Plasma membrane (phospholipids), intracellular organelles
• Energy: Energy stores and insultation (white adipose tissue) (brown adipose tissue - thermogenesis)
• Carriers: Absorption and transport of fat soluble vitamins (A, D, E and K)
• Messengers: Cell signalling
• Prescursors: Chloesterol for many hormones

• Simple
  • Fats - esters of fatty acids with glycerol - oils are fats in the liquid state
  • Waxes - esters of fatty acids with higher molecular weight monohydric alcohols
• Complex 
  • Phospholipids, glycolipids, sulpholipids, aminolipids
• Precursor and derived lipids
  • Fatty acids
  • Glycerol
  • Steroids
  • Hormones

• Triglycerides
  • Main storage forms of fatty acids
• Phospholipids, cholesterol, glycolipids
  • Constituents of membranes
• Sterols - cholesterol
  • Major constituent of plasma membrane, plasma lipoproteins
  • Precursor to vitamin D and many steroid hormones
• Eicosanoids, e.g. Prostaglandins
  • Immune system
  • Inflammation

• Occur mainly as esters in natural fats and oils
• Do occur as free fatty acids
  • Blood
• Are either:
  • Saturated
    • No double bonds in the acyl chain
  • Unsaturated
    • 1 or more double bonds in the acyl chain
• Saturated fatty acids end in -anoic
• Unsaturated fatty acids end in -enoic
• Number of carbons, number of double bonds, lowest carbon number that shows position of the double bond, e.g. Octadecenoic acid 18:1;9

• Butyric acid
  • 4 carbon atoms
  • Present in certain fats such as butter
• Palmitic acid
  • 16 carbon atoms
  • Common in all animal and plant fats

• Oleic acid
  • One double bond
  • Most common fatty acids in natural fats
• Linoleic acid
  • Two/three double bonds
  • Corn, peanut, soybean
• Timnodonic acid - Eicosapentenoic acid
  • 5 double bonds
  • Fish oils
  • Omega 3

• Melting points of even numbered carbon fatty acids
  • Increase with chain length
  • Decrease with increasing unsaturation
• Example
  • A triglyceride with 3 chains, each with 12 carbons and no double bonds is solid at 37 degrees
  • If the fatty acids are 18:2 the lipid is liquid at <0 degrees
• Membrane lipids
  • More unsaturated than storage lipids
    • More fluidic
  • Cholesterol

• Main storage forms of fatty acids
• Esters of glycerol and fatty acids
• Mono- and di- acylglycerides also exist

• Fats have all the available bonding sites taken up by hydrogen
  • Saturated

• Oils have fewer hydrogens on account of the double bonds
  • Unsaturated
  • CH=CH-
  • These are liquid at room temperature

• Plasma membrane is essential for cell integrity
  • Target for drugs
  • Barrier for drugs