JESS'S A LEVELS: Biology: Chapter 2: Biological molecules: Lipids

Biology: Chapter 2: Biological molecules: Lipids

Carboxyl group

Hydroxl group

Series of acids
Contain acidic group (-COOH-) and long hydrocarbon tail (-CH-)
Hydrocarbon chain is usually 15-17 carbon atoms long
Some of the hydrocarbon tails have double bonds between the neighbouring carbon atoms (-C=C-).
Unsaturated: With double bonds - do not contain maximum possible amount of hydrogen. Form unsaturated lipids. Double bonds make fatty acids and lipids melt more easily. Fatty acids/ Lipids with only one double bond are called monounsaturated, one or more double bonds are called polyunsaturated. Examples: Plants lipids - Oils eg olive oil
Saturated: Only single bonds - maximum possible amount of hydrogen. Examples: Animal lipids eg fats

Alcohol: Organic molecule that contains a hydroxyl group (-OH-) attached to a carbon atom.
Ester: Chemical produced in reaction between an acid and alcohol.
Ester bond: Chemical link between acid and alcohol. -COOH- acid reacts with -OH- alcohol to form the ester bond -COO-. Condensation reaction.

Fats and oils
Most common lipid
Glyceride: Ester formed by fatty acid bonding with the alcohol glycerol
Glycerol: Alcohol with 3 hydroxyl groups; each of Glycerol's hydroxyl groups bond with a fatty acid through condensation
Hydrocarbon 'tail' vary in length depending on fatty acids used.
Insoluble in water but soluble in a few organic solvents eg. ethanol and chloroform
Hydrocarbon tails are non-polar (no uneven distribution of electrons) which means they are hydrophobic
Energy reserves: Lipids are better for storing energy than carbohydrates because they have more carbon-hydrogen bonds - Lipids of one mass will yield more energy on oxidation than the same mass of a carbohydrate.
Insulator against loss of heat: Stored around organs and under the skin
Buoyancy for aquatic animals: Blubber
Metabolic source of water: When lipids are oxidised in respiration they are converted to carbon dioxide and water, which is useful for animals in dry climates eg. the desert kangaroo never drinks water but instead relies on this process.

Special type of lipid
One of the three fatty acid 'tails' is replaced with a phosphate group
Phosphates are polar - dissolve in water (hydrophilic)
One end of the lipid is soluble in water - The phosphate group is hydrophilic and makes the head of the phospholipid hydrophilic, but the two remaining fatty acid tails are hydrophobic.
Used to form membranes