3.1.4.1. general properties

• Protein

  • Polymers of amino acids
  • Peptide bond
  • A chain of amino acids bonded together = polypeptide
• Basic structure

  R side chain group varies to form different amino acids

  
• Structures of proteins:

  • Primary - The sequence pf amino acids in the polypeptide chain
  • Secondary - The polypeptide chain twists and folds into a more stable structure (alpha helix or beta pleated sheet). Hydrogen bonds form between C=O and N-H groups.
  • Tertiary - Further twisting and folding. The shape is held by hydrogen, ionic and disulfide bonds. The correct order of amino acids is essential to form the correct tertiary structure.
  • Quaternary - Few proteins have a 4th structure. More than one polypeptide chain bonded together e.g haemoglobin and antibodies
• Test for a protein

  Add Biuret A and then Biuret B

  Shake gently

  Positive result = purple colour change
• What breaks bonds in denaturation?

  Hydrogen bonds break if the temperature rises too high

  Ionic bonds break if the pH changes too much

  Disulfide bonds don't usually break

  Peptide bonds don't break during denaturation
• Examples of functions of proteins

  Enzymes - The shape of the protein must provide a complementary shape to the other molecule

  Antigens - Binding site is complementary to the antigen

  Receptor protein - complementary binding site to hormone/antigen

  Transport protein - binding site complementary to specific molecule