1.3 Lipids

• Triglycerides are made up of 1 glycerol and 3 fatty acids.
• Fatty acids have carboxylic acid groups.
• Saturated - only single carbon (C-C) bonds.
• Unsaturated - at least one double or triple carbon (C=C) bond.
• Polyunsaturated - more than one C=C bond.
• Monounsaturated - one C=C bond.
• Fatty acids contain a variable 'R' group, which contains varying numbers of C and H. It may contain one or more double carbon bonds, may only contain single carbon bonds.
• The R group is the part that determines whether it will be saturated or unsaturated.
• Triglycerides are made up of three fatty acids attached to glycerol by ester linkages.
• Unsaturated fats are liquid because the double bond(s) cause the chain to bend.
• Saturated fats are solid at room temperature as they have no bends in their chains.
• Phospholipid bilayers form cell membranes.
• Triglycerides are not polymers as they are not long chains of monomers (repeating units).
• Triglycerides contain ester bonds between glycerol and three fatty acids.
• The hydrophobic tails of triglyceride molecules repel water, while the polar heads attract it.
• The double carbon bond(s) in unsaturated triglycerides cause the chain to bend so the chains can't fit together neatly, meaning it can't be solid and has to be liquid at room temperature.
• Roles of lipids:

  • energy source
  • protection
  • waterproofing
  • insulation
• Lipids have low melting points due to their nonpolar nature.
• Lipids are a source of energy as when oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release water.
• Lipids are insoluble in water and therefore are useful as waterproofing e.g. plants and insects have waxy lipid cuticles.
• Lipids are used for protection as fat is often stored around the delicate organs such as the kidney.
• Lipids are used as insulation as fats are slow conductors of heat and when stored beneath the body surface, retain heat. They also insulate neurons.
• Lipids have a high ratio of energy storing C-H bonds.
• Lipids have a low mass to energy ratio.
• Lipids are large non-polar molecules.
• Lipids have a high ratio of Hydrogen to Oxygen, which is good for the release of water (important for organisms living in dry climates).
• Being large, non-polar molecules make lipids insoluble so doesn't affect water potential and therefore osmosis.
• Using lipids rather than carbohydrates as an energy store is good because lipids provide more than double the energy and also releases water.
• Phospholipids are made up of 1 glycerol, 1 phosphate, and 2 fatty acids.
• Phospholipids are polar molecules.
• Phospholipids have a hydrophilic phosphate head, which is attracted to water, but does not mix with fat.
• Phospholipids have hydrophobic fatty acid tails, which are repelled by water, but mix with fats.
• Phosphates are attracted to the water in the extracellular and intracellular environments, so the hydrophilic phosphate heads point outwards and the hydrophobic tails point inwards, away from the water.
• Phospholipids tails are non-polar, so no charged molecules can pass through the hydrophobic fatty acid tails.
• Phospholipids allow for the formation of glycolipids (a lipid in the cell membrane with a carb group attached) which are important for cell recognition.
• Phosphate head in phospholipids keep the structure of the cell.
• Triglycerides repel water.
• Test for lipids ----> Emulsion test:

  1. Mix sample with ethanol.
  2. Then mix with water.
  3. Shake.
  4. If lipid present, a white emulsion will form.
• Lipase is an enzyme that breaks down triglycerides into glycerol and three fatty acids.