Fig. 3. Processes of fibrillar self-assembly. The processes that make up the reaction network of filamentous self-assembly fall into two categories, nucleation/multiplication processes, which produce new fibril ends, P, and only a negligible quantity of new fibril mass, and growth processes, which produce fibril mass, M, but leave the fibril number unchanged. The contributions to the rates of growth and nucleation/multiplication are given below the schematic representation for each process. For elongation and secondary nucleation we use two alternative schemes, a single-step and a two-step one. Under certain conditions the single-step description may be sufficient, as discussed in the main text. The rate constants and reaction rates are defined in Table 1.