Lipids

Lipids are macromolecules containing carbon, hydrogen and oxygen

Include triglycerides, steroids, waxes and phospholipids

They are all hydrophobic and insoluble in water

Insolubility a result of their structure

Lipids contain hydrocarbon molecule which contain many non-polar covalent bonds

--> this makes lipids insoluble in water or other polar solvents

Solubility can be improved by combining lipids with other molecules e.g. glycolipids and lipoproteins

Triglycerides and phospholipids are types of glycerides

Triglycerides

Stored as fat in adipose tissue (humans) and as oil (seed of plants)

Fats are liquid at body temperature and solid at room temperature

Oils are liquid at both temperatures

Triglycerides are made by combining three fatty acids with one glycerol

Carboxylic acid group makes up one end of the fatty acid connecting to the glycerol in the condensation reaction

Hydrocarbon tail can be of variable length and contain many carbon atoms joined together

Formed by a process knows as esterification forming an ester bond

An ester bond forms when the hydroxyl (-OH) group of a glycerol molecule bonds with the carboxyl group (-COOH) of a fatty acid

The formation of an ester bond is a condensation reaction

--> for every triglyceride formed, three water molecules are released

Phospholipids

Phospholipids are also formed from glycerol and fatty acids

Contain only two fatty acids bonded to a glycerol molecule

--> the third is replaced by a phosphate ion

The two fatty acids form an ester bond with the glycerol

The phosphate is polar making it hydrophilic and soluble in water

The fatty acid chains are non-polar making it hydrophobic and insoluble in water

Similarities

Both are formed through condensation reactions
Three molecules of water are formed when glycerol forms with fatty acids/phosphate
Both are types of lipids/glycerides
Both have ester bonds

Differences

Triglyceride

Phospholipid