lipids

• lipids are organic molecules with two main types:

  • phospholipids
  • triglycerides
• triglycerides are a good source of energy
• phospholipids have a structural role in cell membranes
• lipids are mainly composed of carbon and hydrogen with some oxygen
• lipids are large and complex macromolecules
• lipids aren't polymers
• lipids are non-polar, meaning they won't dissolve in water
• triglycerides are formed from 1 glycerol and 3 fatty acids
• glycerol is an organic alcohol which has 3 hydroxyl (-OH) groups
• glycerol

  
• fatty acids are organic acids that have a carboxyl (-COOH) group, joined to a hydrocarbon tail.
• fatty acids are a type of carboxylic acid
• the hydrocarbon tail is often represented as 'R'
• An ester bond is the covalent bond formed by a condensation reaction between the -OH group of a carboxylic acid and the -OH group of an alcohol
• a triglyceride is formed by joining one molecule of glycerol to three fatty acids through condensation reactions
• phospholipids are similar in structure to triglycerides apart from one fatty acid is replaced with a phosphate molecule
• the 'head' of the phospholipid (the phosphate and glycerol) is hydrophilic as it has a negative charge.
• the 'tails' of the phospholipid (fatty acids) are hydrophobic as they have no charge
• what is this called?

  A) bilayer

  
• test for lipids:

  1. crush the sample (if solid)
  2. add ethanol and shake
  3. then add water dropwise
  4. a positive results is a white/milky emulsion formed