Help TopicsWebsite FAQGlossaryBrowser CheckService StatusContact Us

Number of Chains (Biological Assembly)

Search for structures based on the number of chains in the biological assembly.

The biological assembly is the arrangement of macromolecules in the structure that is believed to be the biologically meaningful molecular assembly. In structures determined by X-ray crystallography, the biological assembly may contain one copy of the asymmetric unit, multiple copies of the asymmetric unit, or a portion of the asymmetric unit. For more information, click here.

Chains are the individual polymers (macromolecules) contained in a PDB structure. A structure may contain multiple identical chains. Hence, this search option queries for the total number of polymers in the biological assembly, regardless of whether that includes multiple identical molecules.


  1. The biological assembly of the ferritin structure 1AEW is comprised of 24 copies of a single polymer chain.

    Enter "Between 24 and 24" and press "Submit Query" to return all structures that contain exactly 24 chains in the biological assembly. The results include 1AEW.

  2. Enter 100 into the left box, and leave the right box empty. This will query for all structures in the PDB that contain at least 100 chains in the biological assembly.