FIG. 2.

Model of the kinetoplast duplication cycle. T. brucei procyclic forms were prepared for TEM. Images were captured of serial thin sections through kinetoplasts at different stages in their duplication cycle, and 3D reconstructions were generated from these images. (A) The duplication cycle can be divided into five distinct stages, I to V, based on the morphology of the kDNA disk and the replication status of the basal body (bb)/probasal body (pbb) and adjacent flagellar pocket (fp); mm, mitochondrial membrane. bb1 denotes the basal body subtending the mature flagellum, and bb2 is the basal body of the new flagellum. In stage I, the kDNA forms a unit-sized disk; in stage II, the kDNA disk has prominent antipodal sites (AS); stage III kinetoplasts are bilobed and flagellar pocket duplication is complete; stage IV kinetoplasts are connected by a nabelschnur (n); and stage V kinetoplasts (not shown) are morphologically the same as stage I kinetoplasts. (B) Model of a stage IIa kinetoplast superimposed onto a single image from the series (oriented such that the anterior end of the cell is facing right). In this cell, bb2 is in a position anterior to bb1. (C) Model of a stage IIb kinetoplast superimposed onto a single image from the series (oriented as in panel B). In this cell, bb2 is now in a position posterior to bb1. nf, new flagellum; of, old flagellum; r, ridge forming between the old and new flagellar pocket. Scale bars, 200 nm.