2.1.2 (pt2) bio molecules

• lipids make up 5% of cells
• if a lipid is a solid at room temperature it is described as a fat
• if a lipid is a liquid at room temperature it is described as an oil
• functions of lipids:

  • energy storage
  • insulation
  • buoyancy
  • protection
  • regulation of hormones
  • creates hydrophobic membrane
• triglycerides are made up of a glycerol molecule and three fatty acids
• fatty acids have a carboxylic acid group on one end and a hydrocarbon chain (fatty group)
• the fatty acid chains in a triglyceride can be varying lengths
• an essential fatty acid is a fatty acid that cannot be synthesised by the body and is essential in the diet
• fatty acid hydrocarbon chains are usually 2-25 carbons in length
• a saturated fatty acid is a fatty acid chain that has no double bonds between carbon atoms.
• a monosaturated fatty acid is a fatty acid chain that has one double bond between carbon atoms
• a polyunsaturated fatty acid is a fatty acid chain that has more than one double bond between carbon atoms
• unsaturated fatty acids have a different shape to saturated fatty acids as they have kinks or bends due to double bonds between carbon atoms.
• the number of double bonds decrease membrane fluidity and decreases the melting point
• triglycerides are formed by a condensation reaction between a glycerol and 3 fatty acids, an ester bond is formed after the hydroxyl groups interact
• the bonding in triglyceride molecules is covalent
• triglycerides are not considered to be polymers because it has 2 different components (fatty acids and glycerol) and there is no OH group left therefore they cannot form long chains like polymers
• hydrolysis of a triglyceride:

  triglyceride + water -> 3 fatty acids + glycerol (catalysed by an enzyme)
• triglycerides have a large proportion of C-H bonds which when oxidised they release energy, this means triglycerides have a high energy density
• triglycerides are good storage molecules because lipids are insoluble in water so they have no affect on water potential
• fatty acids in an oil are unsaturated and they have a higher proportion of mono and polyunsaturated fatty acids
• fatty acids in a fat are saturated, the more saturated fatty acids the higher the melting point of the fat
• triglycerides are non-polar and hydrophobic
• properties of triglycerides:

  • barrier to entry of larger polar molecules
  • waterproofing leaves
  • good thermal and electrical insulators(subcutaneous fat, and used to insulate neurones)
  • ideal energy storage molecule
• hydrophilic is a charged or polar molecule that can interact with water molecules and is therefore soluble in water
• hydrophobic is a non-polar molecule that cannot interact with water molecules and is therefore insoluble in water
• amphipathic is when a molecule with both hydrophobic and hydrophilic parts
• a phosphate group is an inorganic group containing phosphorous and oxygen
• glycerol is an organic molecule which is a component of triglycerides and phospholipids
• ester bond is a bond between glycerol and fatty acid
• an ester bond is characterised by C double bonded to O and single bonded to another O
• similarities between triglycerides and phospholipids:

  • ester bonds
  • fatty acids
  • produce 3 water molecules in condensation reaction
• differences between triglycerides and phospholipids:

  • phospholipid has a phosphate group
  • phospholipid only has 2 fatty acids but triglycerides have 3
  • triglyceride makes 3 ester bonds and phospholipids only make 2
• saturated fatty acids increase rigidity and increases melting point and decreases fluidity
• longer fatty acids have more intermolecular forces and therefore decreases membrane fluidity
• unsaturated fatty acids increase membrane fluidity
• phospholipids form a micelle if placed in water because water is a polar solvent, the heads are polar and hydrophilic so therefore face outwards, the tails are non-polar and hydrophobic so therefore face inwards
• phospholipids are known as surfactants as they form a layer on the surface of the water with phosphate heads in and tails sticking out
• the role of surfactants in the alveoli prevents the alveoli from collapsing due to creating surface tension and allows them to inflate
• a sterol is a complex alcohol molecule that is based on a four carbon ring structure with an OH group at one end. they have dual hydrophobic and hydrophilic characteristics