Lipids

• What is a triglyceride and how is it formed?


  1 glycerol molecule bonded to 3 fatty acids by ester bonds in a condensation reaction.
• How is an ester bond formed?


  In a condensation reaction, a hydrogen from the glycerol and a hydrogen and an oxygen from the carboxyl group on the fatty acid, react to produce water. An ester bond is then formed between the remaining oxygen atom (glycerol) and carbon atom (fatty acid).
• What is a fatty acid?


  A carboxyl group + hydrocarbon tail (sometimes represented by '-R' )
• Where does variation in fatty acids occur and what can this variation be?

  In the hydrocarbon tail:

  . different lengths of chain

  . saturated (no C=C bonds)

  . unsaturated (C=C bonds present)
• What is the difference between monounsaturated and polyunsaturated fatty acids?


  mono -> 1 C=C bond

  poly -> 2+ C=C bonds
• What is a monoglyceride?


  1 glycerol molecule bonded with just 1 fatty acid by an ester bond.
• How do you form a diglyceride?


  monoglyceride + fatty acid
• Are lipids polymer? Why/why not?

  No - they are not made up of one monomer repeating.
• What is the test (+ results) for lipids?


  Emulsion test - add ethanol + shake, add water + shake

  positive = milky white emulsion

  negative = clear
• What is the potential issue with the test for lipids?

  If the sample is already cloudy, a change could be hard to distinguish.
• What are the useful properties/uses of lipids?


  . energy dense

  . good energy stores

  . good insulators

  . waterproofing

  . make certain hormones

  . phospholipids make up plasma cell membranes
• What are phospholipids made up of?


  1 glycerol molecule bonded to 2 fatty acids by ester bonds. The 3rd fatty acid is replaced by a phosphate group.
• What is the 'head' of a phospholipid and what is significant about it?


  the glycerol + phosphate group

  . it is hydrophilic (attracted to water)
• What are the 'tails' of a phospholipid and what is significant about them?


  the fatty acids

  . they are hydrophobic (repelled by water)
• What causes kinks in phospholipid tails?


  Double carbon bonds
• What happens the more kinks a phospholipid tail has?


  The molecules are harder to pack closely together and so they are less dense and have a lower melting point.
• What are phospholipids the main molecule in?

  The plasma cell membrane
• What is the main use of triglycerides?


  Energy storage
• Are triglycerides soluble or insoluble in water? Why?


  Insoluble as the fatty acid tails are hydrophobic.
• Where are lipids synthesised?


  Smooth ER