L11-12 lipids

• define a lipid

  diverse group of naturally occuring molecules that are soluble in non-polar solvents
• fatty acids are building blocks for complex lipids
• fatty acids are a source of energy
• general structure of fatty acid

  • carboxyl head group (hydrophilic)
  • hydrocarbon tail (hydrophobic)
• amphipathic means

  2 different chemical characteristics
• saturated hydrocarbon means

  no carbon carbon doulbe bonds
• unsaturated hydrocarbon means

  contains carbon carbon double bond
• more unsaturated carbons means

  takes up more space as has kinks in their chains
• cis double bond has hydrogens:

  on same side of the double bond
• trans double bond has hydrogens

  on opposite sides of the double bond
• saturated fatty acid suffix

  anoic
• monounsaturated fatty acid suffix

  enoic
• polyunsaturated fatty acid suffix

  dienoic (for 2); trienoic (for 3) etc
• essential fatty acids are needed because:

  • animals cannot synthesize unsaturated fatty acids
• plants are source of essential fatty acids because they possess the enzymes to synthesize the unsaturated bonds
• 2 types of complex lipids

  • neutral lipids
  • polar lipids
• neutral lipids example


  triacylglycerol
• triacylglycerols contain

  glycerol and 3 fatty acids
• triacylglycerol is storage form of fatty acids because:

  • efficient energy source (better than carbohydrates)
  • major source of biochemical energy
• more bend hydrocarbon fatty acid chain

  compacted less closely, so increase fluidity and lowers melting point
• hydrogenation is the process which

  makes unsaturated oils and fats saturated
• _ double bonds cause bend but _ double bonds do not

  cis and trans
• polar lipids can be based on

  sphingosine or glycerol
• glycerolipids can be

  phosphoglycerides or glycosylglycerides
• structure of phosphoglycerides

  2 fatty acids

  
• phospholipids have 2 ends and have amphipathic properties
• in water phospholipids spontaneously form

  lipid bilayers
• hydrophobic region of phospholipid face

  inwards
• hydrophilic regions of phospholipid face

  outward
• why are bio-membranes important:

  • separate cell contents from surroundings (define the cell)
  • maintain different chemical environments between inside and outside of the cell
  • selectively permeable
• history of models of membrane structure:

  1915:

  • RBCs membranes were isolated and analysed
  • found to contain lipids and proteins

  1925:

  • membranes described as a bilayer of phospholipids

  1935:

  • sandwich model-> bilayer between 2 layers of globular proteins
  • issues->>differ in composition and structure, membrane proteins not very water soluble
• when was the fluid mosaic model proposed?

  1972
• what is the evidence for the fluid mosaic model?

  freeze-fracture of the membrane, membrane proteins bumps into 2 layers
• lateral movement is _

  very fast
• flip-flop movement is _

  quite rare
• lateral movement is _ common than flip-flop

  more
• cholesterol helps _ the membrane

  stabilise
• at high temperatures cholesterol

  reduces movement
• at lower temperature cholesterol

  maintains fluidity
• cholesterol acts as a _ buffer

  temperature