Four Levels of Protein Structure

• The primary structure of a protein is its unique sequence of amino acids

  • peptide bonds link amino acids. The amino end of one peptide is linked to the carboxyl end of another.
• The secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain

  • The coils and folds of the secondary structure result from hydrogen bonds
  • The two shapes are Alpha (α) helix, Beta (β) pleated sheet
• Tertiary Structure is determined by the interactions among various side chains (R Groups)

  • These interactions include hydrogen bonds, ionic bonds, hydrophobic interactions and van der Waals interactions
  • Strong covalent bonds called disulfide bridges reinforce the proteins structure
• Quaternary structure results when two or more polypeptide chains form one macromolecule

  
  

  Examples

  • Collagen is a fibrous protein consisting of three polypeptides coiled like a rope
  • Hemoglobin is a globular protein consisting of four polypeptides, two alpha and two beta chains
• A slight change in primary structure can affect a protein's structure and its ability to function
• Sickle Cell Disease, an inherited blood disease, results from a single amino acid substitution in the protein hemoglobin