Lipids

• Lipids are compounds that are soluble in alcohol but insoluble in water
• Lipids contain:

  • carbon
  • hydrogen
  • smaller amounts of oxygen
• Lipids consists of glycerol and fatty acids
• One glycerol consists on three carbons, three OH groups, and five hydrogen atoms
• Fatty acids consists of a carboxyl end (acid end) and a hydrocarbon tail
• Fatty acids can be saturated or unsaturated
• Describe unsaturated fatty acids:

  • found in plants
  • double bond between two carbons ∴ fewer hydrogen atoms
  • one double bond = monounsaturated
  • more double bonds = polyunsaturated - changes its shape, molecules are further apart, increased fluidity, lower melting point and boiling point
• Describe saturated fatty acids:

  • found in animals
  • molecules are packed closely together, high melting and boiling point
• Glycerol is an alcohol
• Triglycerides are the most common type of lipids in the body
• Triglycerides are macromolecues
• State the functions of Lipids/ Triglycerides:

  • store of energy
  • source of energy for respiration
  • electrical/thermal insulation
  • buoyancy
  • protection
• Explain how lipids store energy:

  They store energy without affecting water potential, preventing osmosis and swelling because its insoluble in water
• Lipids act as a source of energy for respiration
• Lipids are used for buoyancy in adipose tissue which stores fat. Fat is less dense than water
• Lipids are used for protection as they store fat around organs which act as shock absorbers
• Glycerol and fatty acids are joined together by ester bonds: esterification
• Name three types of lipids:

  • triglycerides
  • phospholipids
  • cholesterol - steroids
• Triglycerides consist of one glycerol and three fatty acids
• Phospholipids consist of one glycerol, two fatty acids and a hydrophilic phosphate group
• In phospholipids, one fatty acid contains a phosphoric acid molecule: H3PO4-
• A hydrocarbon tail is amphipathic : a hydrophilic (polar) head and a hydrophobic (non-polar) tail
• Since a hydrocarbon is amphipathic, it may form micelles: tiny balls with tails tucked away inside while the head points outwards towards water
• Steroids/ cholesterol are not made from glycerol and fatty acids
• Steroids/ cholesterol consists of four carbon based rings or isoprene units which are small and hydrophobic
• Steroids/ cholesterol are made in the liver in animals
• Animals in cold environments have less cholesterol in their cell membranes
• State the functions of cholesterol:

  • regulate fluidity
  • produce vitamin D
  • produces bile
  • produces steroid hormones
• Describe cholesterol:

  • four carbon based rings or isoprene units - small and hydrophobic
  • made in the liver in animals
  • makes steroid hormones
  • Function: acts as a buffer, can sit in the middle of a bilayer to the tail or head, increasing the packing of the membrane, to regulate its fluidity, produces vitamin D and bile
  • in plants, stigmasterol (contains a double bond between C22 and C23) is derived from the cell membrane
• What is the name of the test for lipids?

  Emulsion test
• Describe the emulsion test: CHECK MINDMAP

  1. Place the sample in a boiling tube with ethanol
  2. Shake well and leave for 2 to 3 minutes
  3. Pour the solution into a boiling tube containing distilled water
  4. If a lipid is present, a white milky layer will form
• An emulsion is when small droplets of a substance are suspended in another solution
• An emulsion is when small droplets of a substance are suspended in another solution
• Phospholipids are macromolecules
• State the two macromolecules of lipids:

  • Triglycerides
  • Phospholipids
• Lipids do not form polymers
• Cholesterol is a sterol
• Esterification in triglycerides releases three water molecules
• Esterification in phospholipids produces two water molecules
• Lipids can be used for energy storage in the form of triglycerides