One double strand is shown in yellow. A fiber has seven double strands. The fiber model rotates to provide an end-on view. Which now shows a space filling model. We zoom in to observe greater structural detail.
Red lines show how the molecules are paired.
Zooming in on a single molecule shows the polypeptide chain. Contact regions between molecules are color coded. Some mutant forms of hemoglobin affect fiber formation and some do not. We can test he model by seeing if those mutants that affect fiber formation are located at contacts and if those that do not are located away from contacts. If a residue is purple then it affects fiber formation.