Final answer:
In a ribbon model of protein structure, such as the insulin protein, the two parts it is divided into are the α-helices and β-pleated sheets. These represent the secondary structures of the protein that contribute to its overall three-dimensional shape and function.
Step-by-step explanation:
The question seems to be referring to the depiction of protein structures in the context of molecular biology. Specifically, a ribbon model of a protein, like insulin, represents the 3D conformation including elements such as α-helices and β-pleated sheets. These two components are fundamental secondary structures found in proteins. α-helices are characterized by a spiral shape that is stabilized by hydrogen bonds between the backbone atoms in the polypeptide chain. On the other hand, β-pleated sheets are formed by linking two or more segments of the polypeptide chain, which lie parallel to each other, with hydrogen bonds.
Therefore, the two parts that a ribbon is divided into in the context of protein structure would be the α-helical and β-pleated sheet regions. These structures are critical to the protein's function and its interaction with other molecules. To reiterate, the spiral regions on a ribbon model represent α-helix structures and the broad arrows indicate β-pleated sheet structures within the polypeptide chain of the protein.