Lipids contain the elements Carbon Hydrogen Oxygen There are two main groups: Triglycerides Phospholipids

Triglycerides one glycerol molecule 3 fatty acids glycerol fatty acid

OH C C C H H H H H Glycerol C 3 H 8 O 3

Fatty Acids carboxylic acid group (COOH) joined to a long tail of carbon and hydrogen atoms The length of the hydrocarbon tail varies, giving rise to the various fatty acids. The tail is normally written as R, giving the formula R.COOH

Fatty acids Organic acids with a carboxyl (-COOH) group at the end Joined to the carboxyl group is a long hydrocarbon tail This tail differs in each fatty acid The properties of a lipid depend on the fatty acids they contain Fatty acids vary in 2 ways – the length of the HC chain how saturated the molecule is.

C OH O C H H C H H C H H C H H C H H H Fatty Acid R R.COOH COOH

Saturated Fatty Acids All bonds between carbon atoms are single high melting points solids at room temperature associated with animal fats

Unsaturated Fatty Acids One or more double bonds between carbon atoms low melting points liquid at room temperature associated with plant oils

Formation of a triglyceride Formed as a result of 3 condensation reactions between glycerol and 3 fatty acids involving the –OH group of glycerol and the –COOH group of the fatty acid These reactions result in the formation of 3 molecules of water. The bond between glycerol and the fatty acid is called an ester bond.

ester bond C C C H H H H H OH R.COOH glycerol fatty acids OH Formation of a triglyceride HOOC.R condensation H2OH2O H2OH2O H2OH2O C C C H H H H H O O O O O O OC.R triglyceride3 water

Phospholipids Composed of glycerol, 2 fatty acids and a phosphate group. Draw and label diagram p17

Hydrophilic (water loving) head contains glycerol and phosphate group Hydrophobic (water hating) tail contains 2 fatty acids

The glycerol and phosphate part is polar and dissolves in water (hydrophilic) The fatty acids are non-polar and insoluble (hydrophobic) If placed in water the phosphate heads dip into the water and the tails stick out, forming a monolayer Draw diagram page 17

Hydrophilic heads Hydrophobic tails WATER AIR

When shaken in water phospholipids form hollow balls called micelles; the hydrophilic head on the outside and the hydrophobic tails pointing inside.

Phospholipids are important in cell membranes where they form a phospholipid bilayer; a double layer, heads out, tails in. Hydrophilic heads Hydrophobic tails Phospholipid bilayer

Functions of lipids Cell membrane Energy store Insulation Waterproofing/repellent/wax covering on plant cuticle/exoskeletons Buoyancy Protection Storage of fat soluble vitamins