English: Build-Up of Protofilament from the Helical Oligomer The assembly of the helical insulin oligomer (structural nucleus) into a protofilament is shown. Sixteen helical oligomers enter the growing protofilament one by one, and thereby elongate the growing protofilament. It is evident that the oligomer is preshaped for protofilament formation. Individual oligomers are colored on a color scale from dark violet through red, orange, and yellow to white. The eight central oligomers are fully packed against other oligomers, whereas each end of the protofilament has four oligomers that are open to form contacts with further elongating oligomers. For simplicity, only single oligomers are shown entering the protofilament ends. Note that the colloidal coagulation theory, as described by Smoluchowski [56], is compatible with the model. The shape of the oligomer makes it possible that each individual oligomer can associate with either single oligomers or multimers of oligomers, just as multimers of oligomers can associate end to end.