Lipids

• is a variable group
• contains C, H ,O atoms
• high ratio of H:O than carbohydrates
• insoluble in water
• eg triglycerides, phospholipids, cholesterol etc

 

Triglycerides

• they are insoluble in water, but soluble in ethanol
• they are less dense than water (they float)
• act as good insulators – both electrical and thermal.
• contains the molecule glycerol and three fatty acids.
• Three fatty acids and one glycerol molecule join together in a condensation reaction forming ester linkage
• Three molecules of water are released
• The reaction can be reversed using hydrolysis to turn the triglyceride back into its individual molecules

 

Fatty acids

• Have long chains of C and H atoms.
• Saturated fatty acids has only single C-O bonds.
• An unsaturated fatty acid will have carbon-to-carbon (C=C) double bonds
• It makes the molecules in the lipid push apart and so makes them more fluid
• Unsaturated lipids tend to have lower melting points than saturated lipids.

 

Explain how the molecular structure of triglycerides is related to their functions.

• possess hydrophobic tails of fatty acids;
• which cause the molecule to be insoluble in water;
• they are not so easily dissolved out of the cell;
• this functions to provide the properties of the phospholipid bilayer in cell membranes;
• acts as energy store for the cell;
• due to their higher proportion of hydrogen compared to carbohydrates;
• as a result the breakdown of triglycerides yields ore energy;
• due to the lower proportion of oxygen to carbon that requires more oxygen for complete oxidation to occur.
• triglycerides also float in water due to their lighter density;
• this enables them to aid in the buoyancy of aquatic animals;

 

Phospholipids

• one glycerol molecule and two fatty acid molecules bonded to it from condensation reactions, producing these ester bonds.
• a phosphate group is bonded covalently to the third hydroxyl group on the glycerol
• A phospholipid therefore consists of two parts: the phosphate head and the fatty acid tails.
  The head is very hydrophilic (i.e. water-loving) and the tails are hydrophobic (i.e. water-hating)
• In H₂O, phospholipid molecules arrange into a bilayer: hydrophilic heads facing outwards into the water and hydrophobic tails facing inwards, avoiding water.
• This is the basic structure of a cell membrane.

 

Lipids functions

• energy storage
• making biological membranes
• insulation
• protection eg protecting plants from drying up
• boyancy
• acting as hormones