Which amino acid structure creates the characteristic pattern in the electron density map during X-ray crystallography?

The characteristic pattern observed in the electron density map during X-ray crystallography is primarily determined by the backbone structure of the protein. The backbone consists of a repeating sequence formed by the peptide bonds between amino acids, which creates a consistent and regular pattern that can be traced in the electron density map. This backbone arrangement allows researchers to derive the overall fold and geometry of the protein structure, as it outlines the main chain trajectory.

While individual amino acids and side chains contribute to the final electron density observed, it is the backbone that is essential for establishing the foundational pattern. The side chains do introduce variations in the density due to their unique chemical properties, but the overarching framework that guides structure determination is dictated by the backbone conformation. X-ray crystallography primarily captures this backbone orientation, establishing a core representation of how proteins are structured in three-dimensional space.