Lipids + water + inorganic ions

• Describe how to test for lipids in a sample

  .

  1. dissolve samples in ethanol
  2. add an equal volume of water and shake
  3. positive result: milky white emulsion forms
• How do triglycerides form?

  Condensation reaction between 1 molecule of glycerol & 3 fatty acids forms ester bonds
• Compare saturated and unsaturated fatty acids

  saturated

  • contain only single bonds
  • straight-chain molecules have many contact points
  • higher melting point = solid at room temperature
  • found in animal fats

  Unsaturated

  • contain C=C double bonds
  • 'Kinked' molecules have fewer contact points
  • Lower melting point = liquid at room temperature
  • Found in plant oils
• Relate the structure of triglycerides to their functions

  .

  • high energy:mass ratio = high calorific value from oxidation (energy storage)
  • insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing
  • slow conductor of heat = thermal insulation
  • less dense than water = buoyancy of aquatic animals
• Describe the structure and function of phospholipids

  Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head

  • forms phospholipid bilayer in water = component of membranes
  • tails can splay outwards = waterproofing
• Compare phospholipids and triglycerides

  .

  • both have glycerol backbone
  • both may be attached to a mixture of saturated, monounsaturated & polyunsaturated fatty acids
  • both contain the elements C,H,O
  • both formed by condensation reactions
• Contrast phospholipids and triglycerides

  .

  phospholipids

  • 2 fatty acids & 1 phosphate group attached
  • hydrophilic head & hydrophobic tail
  • used primarily in membrane formation

  triglycerides

  • 3 fatty acids attached
  • entire molecule is hydrophobic
  • used primarily as a storage molecule (oxidation releases energy)
• Are phospholipids and triglycerides polymers?

  No - they are not made from a small repeating unit. They are macromolecules
• Why is water a polar molecule

  O atoms are slightly negatively charged. H atoms are slightly positively charged

  the polarity of water molecules means that a hydrogen atom on one water molecule is attracted to the oxygen atom on another water molecule

  this attraction is called hydrogen bonding
• 4 biologically important properties of water

  .

  • metabolite / solvent for chemical reactions in the body
  • high specific heat capacity
  • high latent heat of vapourisation
  • cohesion between molecules
• Explain why water is significant to living organisms

  .

  • Solvent for polar molecules during metabolic reactions
  • enables organisms to avoid fluctuations in core temperature
  • cohesion-tension of water molecules in transpiration stream
• What are inorganic ions and where are they found in the body?

  .

  • ions that do not contain carbon atoms
  • found in cytoplasm & extracellular fluid
  • may be in high or very low concentrations
• Explain the role of hydrogen ions in the body

  .

  • high concentration of H+ = low pH (acidic)
  • H+ ions interact with H-bonds & ionic bonds in tertiary structure or proteins, which can cause them to denature
• Explain the role of iron ions in the body

  .

  • Fe2+ bonds to porphyrin ring to form haem group in haemoglobin
  • haem group has binding site to transport 1 molecule of O2 around body in bloodstream
  • 4 haem groups per haemoglobin molecule
• Explain the role of sodium ions in the body

  .

  • Involved in co-transport for absorption of glucose & amino acids in lumen of gut
  • involved in propagation of action potentials in neurons
• Explain the role of phosphate ions in the body

  component of:

  • DNA
  • ATP
  • NADP
  • cAMP