FIGURE 4.

“Thread-grain” transition of mitochondria: swelling versus fission. (A and B) Model mitochondria shortening from l = 2.5 μm and d = 0.34 μm due to swelling (A) or fission (B). (C and D) Diameters of model mitochondria calculated as a function of length, based on the considerations of constant n and s_total for swelling (C) and constant v_total and s_total for fission (D). (E) v_total as a function of length during swelling. (F) Number of mitochondria as a function of length during fission (the starting n was 100). (G and H) Thinness ratios obtained by filtering blurred model mitochondrion images generated with the parameters given in C–F using filter functions shown in Fig. 2 D. Traces from top to bottom in C–E, and from bottom to top in F–H correspond to the starting diameters (in μm) 0.44, 0.40, 0.36, 0.32, 0.30, 0.28, 0.26, and 0.22, or to s_total/v_total ratios (constant for fission and initial for swelling from l = 7.5 μm) of (in μm⁻¹) 9, 10, 11, 12.3, 13, 14, 16, and 19. The simulation of mitochondrial swelling was started from l = 7.5 μm (black traces) and alternatively from l = 2.5 μm (gray traces) with the same starting diameters as given above. The results of the fission simulation are fully determined by the constant s_total and v_total, and therefore do not depend on the initial length.