Proteins

Proteins

1. Held by peptide bonds

2. Amino acids -> polypeptide chains

   • held together by 4 other bonds
     • Disulfide bonds
     • Ionic bonds
     • Hydrogen bonds
     • Hydrophobic Interactions

3. 4 levels of protein structure

   • Primary
     • Simple linear sequence of amino acid residues attached together by peptide bonds
   • Secondary
     • Bendings and foldings due to presence of hydrogen bonds at regular intervals between the -CO and -NH groups of the peptide bonds
     • Polypeptide chains coil to form alpha-helix and beta-pleated sheets
   • Tertiary
     • The irregular manner in which the helical and non-helical regions of a polypeptide are folded to form a precise, compact globular structure
     • E.g. Myoglobin
   • Quaternary
     • The interaction between more than one polypeptide chains to form an intact functional protein
     • E.g. Haemoglobin

4. Properties

   • Colloidal Properties: very large molecules
   • Amphipathic Properties
   • Electric Properties: from charged R groups
   • Specific 3D Conformation

5. Denaturation

   • The loss in 3D comformation by the breaking of bonds
   • Weak interactions (H-bonds) are destroyed
   • Unfolding of the structure - mildly denatured
   • Renaturation is possible , allowing proteins to return to its normal shape and regain its properties
   • If irreversible, protein molecule loses its biological functions
   • Denatured proteins form large aggregates precipitate (coagulation)