Biology 3.4 Lipids

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Lipids have following characteristics:

  • Carbon, hydrogen and oxygen.
  • Proportion of oxygen to carbon and hydrogen smaller than in carbohydrates.
  • Insoluble in water.
  • Soluble in organic solvents.

Main groups = triglycerides (fats and oils), phospholipids and waxes.

Roles of lipids

Plasma membranes - phospholipids = flexibility of membranes and transfer of lipid-soluble substances across them.

Other roles:

  • Energy source - when oxidised provide more than twice the energy of carbohydrates.
  • Waterproofing - insoluble, both plants and insects have waxy cuticles, mammals produce oily secretion from sebaceous glands.
  • Insulation = fats are slow conductors of heat.
  • Protection - stored around delicate organs.

Fats are solid at room temp, oils are liquid.

Triglycerides = 3 fatty acids with glycerol, each fatty acid forms…


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