PROTEINS

• Amino acid structure


  -Amine group (-NH2)

  -Carboxyl group (-COOH)

  -Hydrogen atom

  -R Group- variable

  
• Peptide bond


  Bond between two amino acids formed by a condensation reaction, can be broken by hydrolysis.
• Primary structure of proteins

  -Sequence of amino acids joined together by condensation reactions in polymerisation

  -Forms a polypeptide

  -Sequence determined by DNA

  -Determines ultimate shape and hence its function
• Secondary structure of proteins

  -H bonds

  -Cause polypeptide chain to twist into a 3D shape

  -A helix or B sheet
• Tertiary structure of proteins

  -Polypeptide chains twisted even more to give complex specific 3D structures

  -Maintained by different bonds:

  Disulphide bridges, iconic bonds, H bonds
• Quaternary structure of proteins


  -Multiple polypeptide chains

  -Non-protein (prosthetic) groups associated (e.g. haem group in haemoglobin)
• Test for proteins

  Biuret test- detects peptide bonds:

  • Place a sample of solution to be tested in a test tube, add equal volume of NaOH at room temp
  • Add a few drops of very dilute copper (II) sulphate solution and mix gently
  • Purple colour indicates a positive result, if no protein then solution remains blue