Protein Structure

Protein Structure

1. Primary

   • sequence of AAs
   • peptide bond
     • form by condensation reaction
     • partial double-bond charater
     • Rigid and planar
     • Trans configuration
     • Uncharged and polar

2. Secondary

   • alpha-helix
     • formed by H bonds between AAs
     • right-handed spiral conformation
       • tightly packed
       • side chains extend outwards
     • Keratin and myoglobin have many
     • H bonds are weak individually
       • collectively stabilise the alpha-helix
       • more flexibility
     • some AAs are incompatible with alpha-helix
       • proline
         • its secondary amide group is part of a 5-member ring
       • charged AAs
         • form ionic interactions
         • create electrostatic repulsion
       • AAs with bulky side chains
         • tryptophan
         • sterical hindrance
           • means the side chain is blocking formation

3. Tertiary

   • Bonds
     • Stabilised by hydrophobic interactions
       • Between non-polar AAs in the interior of the protein
         • E.g. disulphide bond between 2 cystines
     • Stabilised by ionic and hydrophilic interactions
       • Between charged or polar AAs

4. Quaternary

   • Formed from several similar or unrelated polypeptides
   • Non-covalent interactions hold the polypeptides together
   • Subunits can function independently or in a cooperative way