Lipids, water and inorganic ions

• Describe how to test for lipids in a sample

  ~Dissolve solid samples in ethanol

  ~Add an equal volume of water and shake

  ~Postive result = milky white emulsion forms
• How do triglycerides form

  Condensation reaction between one molecules of glycerol and three fatty acids forms ester bonds
• Contrast 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

  ~Insoluble hydrocarbon chain = no effect on water potential of cells and 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 two hydrophobic fatty acid tails and one 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, monosaturated and polysaturated fatty acids

  ~Both contain the elements C,H,O

  ~Both formed by condensation reactions
• Contrast phospholipids and triglycerides

  Phospholipids

  ~Two fatty acids and one phosphate group attached

  ~Hydrophilic head and hydrophobic tail

  ~Used primarily in membrane formation

  Triglycerides

  ~Three fatty acids attached

  ~Entire molecule is hydrophobic

  ~Used primarily as a storage molecule
• Why is water a polar molecule

  O is more electronegative than H, so attracts the electron density in the covalent bond more strongly
• State four biologically important properties of water

  ~Metabolite/ solvent for chemical reactions in the body

  ~High specific heat capacity

  ~High latent heat capacity

  ~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 and 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

  ~H+ ions interact with H-bonds and ionic bonds in tertiary structure of 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 one molecules of O2 around body in bloodstream
• Explain the role of sodium ions in the body


  ~Involved in co-transport for absorption of glucose and amino acids in lumen of gut

  ~Involved in propagation of action potentials in neurons
• Explain the role of phosphate ions in the body

  ~DNA

  ~ATP

  ~NADP

  ~cAMP