What are macromolecular structures known for?

Macromolecular structures are characterized by their large size and the way their atoms are bonded together, primarily through covalent bonds. This extensive network of covalently bonded atoms leads to the formation of giant structures, which can display a variety of properties such as strength, rigidity, and stability. Examples of macromolecular structures include polymers like polyethylene and protein molecules, which consist of long chains of repeating units or complex arrangements of atoms.

In contrast to other choices, macromolecular structures generally do not have low boiling and melting points; they often require substantial energy to break the strong covalent bonds that hold them together. Additionally, they may not always be soluble in water, as many of these large molecules are hydrophobic or may not interact favorably with water. Finally, the characteristic bonding in macromolecules is primarily covalent, rather than metallic, which is typical of metals and their alloys. Thus, the defining feature of macromolecular structures is indeed their formation of giant, covalently bonded networks.