Figure 1. Large-scale structure of mitochondria.

(A) Confocal micrograph (cross-section through cellular body) visualizing the mitochondrial network (scale bar is 1.3 µm) in a HeLa cell. (B) Result of thresholding and skeletonization of the reticulum in (A). Upper rectangle: decomposition of the reticulum into a set of interconnected linear segments. Lower inset: positions of detected degree k = 1 (magenta) and 3 (blue) network nodes. (C) Graph representation of the mitochondrial reticulum using three node types: k = 1 (magenta), 2 (green) and 3 (blue). The reticulum can be represented as a set of linear segments consisting of one or more edges (black rods) liking the nodes. (D) Two types of elementary network transformations comprising the reticulum fission/fusion reactions. (E) Segment types present in the network: (1-1) separate open-end segments, (2-2) separate loop segments, (1-3) surface and (3-3) internal segments of branched clusters.