Protein structure refers to the arrangement of atoms in an amino acid-chain molecule. There are four levels of structure to distinguish:

  • Primary
    The primary structure of a protein is the sequence in which amino acids form a polyeptide chain held together by peptide bonds.

  • Secondary
    The secondary structure refers to the spatial conformation of the central or backbone polyeptide chain. Without the side chains, these structures typically include α‐helices, β‐sheets, and turns.

  • Tertiary
    The tertiary structure is about the arrangement of a three dimensional structure which is formed by the folding of α‐helices and β‐sheets from the secondary structure.

  • Quaternary structure
    Many types of proteins consist of two (or more) polypeptide chains called subunits. The way that these subunits are aggregated is referred to as the quaternary structure.

The protein structure is important as it sets the foundation for its interaction with other molecules. In other words, the structure determines protein functions such as transportation and storage, energy, the creation of hormones and repair and maintenance.

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