• A polypeptide chain will fold differently due to the interactions (and hence the bonds that form) between?R groups. The three-dimensional configuration that forms is called the?tertiary structure?of a protein
• Each of the?twenty amino acids?that make up proteins has a unique?R group?and therefore many different interactions can occur creating a vast range of protein configurations and therefore functions
• Within tertiary structured proteins are the following bonds:
  • Strong covalent?disulphide
  • Weak?hydrophobic interactions
  • Weak?hydrogen
  • Ionic

   

The interactions that occur between the R groups of amino acids determines the shape and function of a protein. These interactions are found within tertiary structures of proteins

Disulphide

• Disulphide bonds?are?strong?covalent bonds that form between?two cysteine R groups?(as this is the only amino acid with?an available sulphur atom?in its R group)
• These bonds are the strongest within a protein, but occur less frequently, and help stabilise the proteins
• These are also known as disulphide bridges
• Can be broken by oxidation
• Disulphide bonds are common in proteins secreted from cells eg. insulin

Ionic

• Ionic bonds?form between?positively charged?(amine group -NH₃⁺) and?negatively charged?(carboxylic acid -COO^-)?R groups
• Ionic bonds are stronger than hydrogen bonds but they are not common
• These bonds are broken by pH changes

Hydrogen

• Hydrogen bonds?form between strongly polar?R groups. These are the weakest bonds that form but the most common as they form between a wide variety of R groups

Hydrophobic interactions

• Hydrophobic interactions?form between the?non-polar (hydrophobic) R groups?within the interior of proteins

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