Quaternary structure

• why are some polypeptide chains not functional?

  sometimes they are not functional unless they are in combination
• what might some polypeptide chains do in order to become functional?

  • in some cases, they might combine with another polypeptide chain, such as the insulin molecule, which has 2 chains
  • they might also be also be associated with non-protein groups and form large, complex molecules, such as haemoglobin