Proteins

 

  • Proteins are long chains of amino acids.
  • Each amino acid is composed of an organic molecule with a carboxyl end and an amino end
    • Proteins form when amino acids are joined together by dehydration synthesis, i.e. the hydrogen from the amino end of one molecule combines with the hydroxyl group of the carboxylic acid end of another amino acid molecule..
    • This bond is called a peptide bond and the compound formed is called a peptide.
    • The lengths of polypeptide chains vary widely fromas short as 9 amino acid to thousands of amino acids.
    • Polypeptides with more than 100 amino acid residues are called proteins.

    • The structure of the protein can be described at four levels.
    • Primary Structure is the sequence of amino acids.
    • Secondary Structure arises through the formation of hydrogen bonds forming a helix.
    • Tertiary Structure Apart from the simple twisting, most of the polypeptide chains twist on themselves (mostly through further hydrogen bonding) to form tertiary structures.
    • Some functional proteins are infact composed of two or more separate chains (e.g. insulin and hemoglobin). This is the quaternary structure of the protein.
    • On denaturing (either by heat or chemicals), proteins retain their primary structure but lose their secondary, tertiary and quaternary structures. This would usually cause them to alter their physical properties including function.