What type of bonds stabilize protein tertiary structure?

Understanding:

•  The secondary structure is the formation of α-helices and β-pleated sheets stabilised by hydrogen bonding

    
Secondary (2º) Structure

• The secondary structure is the way a polypeptide folds in a repeating arrangement to form α-helices and β-pleated sheets
• This folding is a result of hydrogen bonding between the amine and carboxyl groups of non-adjacent amino acids
• Sequences that do not form either an alpha helix or beta-pleated sheet will exist as a random coil
• Secondary structure provides the polypeptide chain with a level of mechanical stability (due to the presence of hydrogen bonds)
• In pictures, alpha helices are represented as spirals (purple ; left) and beta-pleated sheets as arrows (blue ; right)

Understanding:

•  The tertiary structure is the further folding of the polypeptide stabilised by interactions between R groups

    
Tertiary (3º) Structure

• The tertiary structure is the way the polypeptide chain coils and turns to form a complex molecular shape (i.e. the 3D shape)
• It is caused by interactions between R groups; including H-bonds, disulfide bridges, ionic bonds and hydrophobic interactions
• Relative amino acid positions are important (e.g. non-polar amino acids usually avoid exposure to aqueous solutions)
• Tertiary structure may be important for the function of the protein (e.g. specificity of active site in enzymes)

Understanding:

•  The quaternary structure exists in proteins with more than one polypeptide chain

    
Quaternary (4º) Structure

• Multiple polypeptides or prosthetic groups may interact to form a single, larger, biologically active protein (quaternary structure)
• A prosthetic group is an inorganic compound involved in protein structure or function (e.g. the heme group in haemoglobin)

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