<prompt> The assembly of secondary structural units into larger functional units such as the mature polypeptide and its component domains isPrimary structureSecondary structureTertiary structureQuaternary structure  <response>: The modular nature of protein synthesis and folding are embodied in the concept of orders of protein structure: Primary structurethe sequence of amino acids in a polypeptide chainSecondary structurethe folding of short 3-30 residue, contiguous segments of polypeptide into geometrically ordered units.Tertiary structurethe assembly of secondary structural units into larger functional units such as the mature polypeptide and its component domains.Quaternary structurethe number and types of polypeptide units of oligomeric proteins and their spatial arrangement.Ref: Harpers illustrated biochemistry. 30th edition page no: 37 