Biology 3.4 Lipids

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…