Lipids

What are lipids?

• A macromolecule

• Made of C, H and O

• Can exits as fats, oils and water

• Insoluble in water, soluble in alcohol and other lipids

• Good source of energy (44J/Kg)

• Produce more ATP than glucose during lipid respiration, they can also be stores of energy

• Poor conductors of heat

• Most fats and oils are triglycerides

What is a triglyceride?

• Formed by a condensation reaction between 4 components:

  • 3 fatty acids

  • 1 glycerol

• Fatty acid:

  • Carboxyl group (-COOH)

  • Attached to a long, non-polar hydrocarbon

  • Saturated (C-C)

  • Unsaturated (C=C)

What is the effect of saturation on a triglyceride?

• More saturated = more dense

• Increasing double bonds introduces ‘kinks’ into the molecules, this reduces density as there will be more space between the hydrocarbons

• Animal fats tend to be saturated and plant fats tend to be unsaturated

Condensation reaction between glycerol and a fatty acid

Phospholipids

• One fatty acid can be replaced by a polar phosphate group

• Hydrophilic head

• Hydrophobic tail

• Membrane lipids are a amphipathic

• Partially permeable helps control movement of substance across the cell

Function of lipids

• Protection of vital organs- acts like a shock absorber

  • Some bacteria have a lipid layer to act as a protective capsular layer

• Prevent evaporation in plants and animals

• Insulate the body- as a heat insulator

• Form the myelin sheath around some neurones- electrical insulators

• As a water source (respiration of lipids- which provides a lot of ATP)

• Metabolic water- water produced by respiration

• Component of cell membranes

• Makes some hormones e.g testosterone

Cholesterol

• Used to synthesise steroid hormones: testosterone and oestrogen

• Synthesises vitamin D

• Regulates fluidity of cell membranes and acids mechanical stability

• Made up of 4 isoprene rings

• Not based on fatty acids and glycerol

• Plant membranes have a cholesterol derivative called stigmasterol

Food test for lipids

Emulation test:

• Add water and ethanol to the solution

• Shake vigorously for 10 seconds

• Positive- milky white emulsion appears

• Negative- emulsion doesn’t for, it’ll look like separate layers if liquids are of different densities