What is true about proteins? In the tertiary structure, we observe the polypeptide chain, with multiple fundamental structures, adopt a folded heterogeneous shape that is essential for the optimal functioning of the protein. Every single one of this irregular structures are called "domains", and they usually have one specific action in the whole protein complex In the tertiary structure, we observe the polypeptide chain, with multiple fundamental structures, adopt a folded homoogeneous shape that is essential for the optimal functioning of the protein. Every single one of this regular structures are called "domains", and they usually have one specific action in the whole protein complex In the quaternary structure, we observe the polypeptide chain, with multiple fundamental structures, adopt a folded homoogeneous shape that is essential for the optimal functioning of the protein. Every single one of this regular structures are called "domains", and they usually have one specific action in the whole protein complex In the quaternary structure, we observe the polypeptide chain, with multiple fundamental structures, adopt a folded heterogeneous shape that is essential for the optimal functioning of the protein. Every single one of this irregular structures are called "domains", and they usually have one specific action in the whole protein complex