Lipids
Like carbohydrates, lipids contain carbon, hydrogen and oxygen but much less oxygen. They are non-polar compounds and so are soluble in water but dissolve in organic solvents, such as propanone and alcohols.
Triglycerdes
Phospholipds
Formed by combination of 1 glycerol molecule and 3 fatty acid molecules.
Glycerol molecule in a lipid always same but fatty acid component varies.
Fatty acids join together by glycerol condensation reactions, whereby 3 molecules of water are removed and ester bonds are formed between the glycerol and fatty acid.
Each molecule has 1 end that is water soluble. Polar head is hydrophilic (interacts with water) and non-polar tail is hydrophobic (does not interact wth water).
Waxes
Melt above 45 degrees C and have a waterproofing role in animals and plants.
Properties
Roles of lipids
Test for fats/oils
Phospholipids in biological membranes and for electrical insulation (the myelin sheath that surrounds the axons of nerve cells
Triglycerides for energy reserve in plants and animals, thermal insulation, protection (fat stored around organs) and metabolic water reduced in chemical reactions
Waxes for waterproofing in terrestrial organisms, waxes reduce water loss.
If hydrocarbon chain has only single carbon-carbon bonds then the fatty acid is saturated because all carbon atoms are linked to max number of hydrogen atoms.
Molecules align so fats are solid They remain solid at body temp so useful for storage in mammals.
If bond is single, the molecule I unsaturated and has a kink. The molecules cannot align and the lipid cant solidify. Unsaturated fats are oils which remain liquid at room temp.
Sample to be tested mixed with ethanol which dissolves any lipids present.
Shaken with equal volume of water. The dissolved lipids come out of solution as they are not soluble in water. The form an emulsion which makes the sample cloudy white.