Generalities about fats and lipids: Phospholipids


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One of the principal types of lipid in the membrane include the phospholipids. These have a polar head group and two hydrocarbon tails.


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An example of a phospholipid is shown in this figure (right). The top region beginning with the NH3 is the polar group. It is connected by glycerol to two fatty acid tails. One of the tails is a straight chain fatty acid (saturated). The other has a kink in the tail because of a cis double bond (unsaturated).This kink influences packing and movement in the lateral plane of the membrane.
Phospholipids pack together in two leaflets in the membrane. The presence of the cis double bonds prevents tight packing and makes the bilayer difficult to freeze. The lipid bilayer gives the membranes its fluid characteristics.
At low temperatures, the bilayer is in a gel state and tightly packed. At higher (body) temperatures, the bilayer actually "melts' and the interior is fluid allowing the lipid molecules to move around, rotate, exchange places. This also allows movement of other components of the membrane.
Phospholipid structure
Membrane with double phospholipid layer
Most common phospholipids

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Phosphoglycerides containing one nitrogenous base:

  • Choline glycerophospholipids (PC)
  • Ethanolamine glycerophospholipids (PE)
  • Serine glycerophospholipids (PS)
  • Glycine glycerophospholipids (PG)

Phosphoglycerides containing two glycerol molecules:

  • Phosphatidylglycerol
  • Diphosphatidylglycerol or Cardiolipin
  • Lysobisphosphatidic acid

Phosphoglycerides containing inositol: Phospho-inositides

More details can be found in the amazing pages of the CyberLipid Center.