1.5 - Lipids

• characteristics of lipids

  contain carbon, hydrogen, and oxygen

  insoluble in water

  soluble in organic solvents - alcohols, acetone
• types of lipids

  triglycerides (fats and oils)

  phospholipids

  waxes
• roles of lipids

  contribute to flexibility of cell membranes and transfer of liquids across them

  source of energy - provide lots of energy when oxidised

  waterproofing - as they're insoluble in water

  insulation - slow conductors, electrical insulators (myelin sheath)

  protection - fat stored around delicate organs
• structure of tryiglycerides

  3 fatty acids bonded to a glycerol with an ester bond formed during a condensation reaction

  fatty acid tail is hydrophobic

  
• the condensation reaction to form triglycerides is between

  carboxylic acid group of fatty acid

  hydroxyl group of glycerol
• basic structure of a fatty acid

  hydrocarbon tail varies

  
• are triglycerides a polimer? why?

  not a polymer because it's not made of repeating units - it's a macromolecule
• what makes different fats and oil have different properties

  variations in the fatty acids
• saturated fatty acids

  fatty acid doesn't have any c=c double bonds

  they are saturated with hydrogen atoms
• monounsaturated faty acids

  fatty acids with a single double bond
• polyunsaturated fatty acids

  fatty acids with more than one double bond

  causes molecule to bend (it's more flexible) so it can't pack together too closely so it's liquid at room temperature
• how the structure of triglycerides is related to its properties

  . high ratio of energy-storing carbon-hydrogen bonds to carbon atoms so are a good store of energy

  . low mass to energy ratio so can be stored in small volumes

  . large, non-polar molecules so are insoluble so storing it won't affect water potential

  . release water when oxidised because of high ratio of hydrogen to oxygen atoms so are an important source of water
• structure of phospholipids

  made of a phosphate group, glycerol and 2 fatty acids

  phosphate head is hydrophilic so interacts with water but not fat (polar)

  fatty acid tail is hydrophobic so interacts with fat but not water

  
• how the structure of phospholipids is related to its properties

  . polar molecule (hydrophilic head, hydrophobic tail) so in aqueous environment it forms a bilayer in cell membranes

  . hydrophilic head helps to hold at the surface of cell membranes

  . centre of bilayer is hydrophobic so soluble substances can't pass

  . allows to form glycolipids by combining with carbohydrates in cell membrane
• test for lipids

  emulsion test:

  use a completely dry, grease-free test tube and add 2cm^3 of sample and 5cm^3 of ethanol

  shake test tube to dissolve sample in ethanol

  add 5cm^3 of water and shake gently

  milky-white emulsion means there are lipids