Lipids

• Triglycerides are macromolecules- they're complex molecules with a relatively large molecular mass
• They contain carbon, hydrogen and oxygen
• Triglycerides have one molecule of glycerol with 3 fatty acids attached to it
• They have long tails made of hydrocarbons which are hydrophobic which make lipids insoluble in water
• Triglycerides are synthesised by the formation of an ester between each fatty acid and the glycerol molecule
• each ester bond is formed by a condensation reaction
• the process in which triglycerides are synthesised is called esterification
• triglycerides break down when the ester bonds are broken with a hydrolysis reaction
• saturated fatty acids don't have any double bonds between the carbon atoms
• unsaturated fatty acids have at least one double bond between carbon atoms.
• Phospholipids are also macromolecules. similar

  to triglycerides except one of the fatty acid molecules

  is replaced by a phosphate group.
• the phosphate group is hydrophilic (it attracts water

  molecules) and the fatty acid tails are hydrophobic.
• label the structure

  A) fatty acid

  B) fatty acid

  C) fatty acid

  D) glycerol

  E) triglyceride

  
• label the structure

  A) phosphate group

  B) glycerol

  C) fatty acid

  D) fatty acid

  E) phospholipid

  
• in animals and plants triglycerides are used as energy storage molecules and some bacteria use triglycerides to store energy and carbon
• Triglycerides are good for storage because:

  • long hydrocarbon tails- contain a lot of chemical energy and most released when broken down so lipids contain 2x energy /g than carbs
  • insoluble- water dosen't enter cell by osmosis which would make them swell as tails are hydrophobic
• phospholipids are found in the cell membrane of all eukaryotes + prokaryotes and make up the phospholipid bilayer
• • Phospholipid heads are hydrophilic and their tails are hydrophobic, so form a double layer with their heads facing out to the water.
  • The centre of the bilayer is hydrophobic, so water-soluble substances can’t easily pass through it — the membrane acts as a barrier to those substances.
• • Cholesterol - has a hydrocarbon ring structure attached

  to a hydrocarbon tail. The ring structure has a polar hydroxyl (OH) group attached

  • In eukaryotic cells they help to regulate the fluidity of the

  cell membrane by interacting with the phospholipid bilayer.
• features of cholesterol:

  • small and flat shape- so it can fit between phospholipids in the membrane
  • at high temps they bind to hydrophobic tails of phospholipids so they pack closer together making membrane less fluid and more rigid
  • at low temps prevents phospholipids packing to close together so increases membrane fluidity