Final answer:
Insulin has a complex structure that involves primary, secondary, tertiary, and quaternary levels, with its three-dimensional tertiary structure being essential for its biological function.
Step-by-step explanation:
The structure of insulin can be described in terms of primary, secondary, tertiary, and quaternary levels. The primary structure refers to its amino acid sequence. Insulin exhibits a secondary structure through regions of alpha-helices and beta-sheets. The tertiary structure of insulin is its unique three-dimensional shape resulting from the folding of the protein, and is essential for its biological function. Finally, insulin may also exhibit a quaternary structure when two insulin monomers (A and B chains) come together, stabilized by disulfide bonds and other interactions, as seen in its storage form within the body.