Protein Interactions (AQA A Level Biology): Revision Note

Proteins: interactions & bonds

• A polypeptide chain will fold differently, into its tertiary structure, due to the interactions (and hence the bonds that form) between R groups

• 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 disulfide

  • Weak hydrophobic interactions

  • Weak hydrogen

  • Ionic

Disulfide

• Disulfide bonds (also known as disulfide bridges) are strong covalent bonds that form between two cysteine R groups (this is the only amino acid with an available sulfur atom in its R group)

• These bonds are the strongest within a protein, but occur less frequently, and help stabilise the proteins

• They can be broken by reduction

• Disulfide bonds are common in proteins that are secreted from cells e.g. 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