proteins

• how are polypeptides formed?

  • condensation reaction
  • forming peptide bonds
• primary structure of protein


  • sequence of amino acids in a polypeptide
  • determined by dna base sequence
• secondary structure of protein


  • folding of polypeptide chain
  • into alpha helix or beta pleated sheet
  • held by hydrogen bonds
• alpha helix

  • NH bonds on the same side
  • spiral
  • Hydrogen bonds parallel to axis
• beta sheet


  • NH and CO bonds alternate
• tertiary structure of protein


  • 3D folding of the polypeptide chain
  • held by hydrogen, disulphide bridge and ionic bonding
• quaternary structure


  • 2 or more polypeptide chains
  • folded into a protein
  • held by same bonds as tertiary structure
  • addition of prosthetic group
• globular proteins


  • tertiary and quaternary structure protein
  • spherical
  • compact
  • hydrophillic group outwards
  • e.g haemoglobin
• fibrous proteins


  • form long chains and fibres
  • amino acid sequence repeats
  • insoluble in water
  • e.g collagen
• collagen


  • fibrous protein
  • component of bone, tissue and cartilage
  • 3 polypeptide chains
  • joined by hydrogen and covalent bonds
  • cross linked - providing strength
• haemoglobin 


  • globular protein
  • bind to oxygen at varying affinity to transport it around blood
  • 2 alpha and 2 beta chains
  • 4 prosthetic haem groups
  • haem groups form coordinate bond with oxygen