Trypanosome mitochondria

Eukaryotic cells also have organelles, mitochondria (Fig. 24-6) and chloroplasts, that contain DNA. Mitochondrial DNA (mtDNA) molecules are much smaller than the nuclear chromosomes. In animal cells, mtDNA contains fewer than 20,000 bp (16,569 bp in human mtDNA) and is a circular duplex. Each mitochondrion typically has two to ten copies of this mtDNA molecule, and the number can rise to hundreds in certain cells when an embryo is undergoing cell differentiation. In a few organisms (trypanosomes, for example) each mitochondrion contains thousands of copies of mtDNA, organized into a complex and interlinked matrix known as a kinetoplast. Plant cell mtDNA ranges in size from... 

While a DNA molecule may exist as a straight rod, the two ends are often covalently joined. Thus, the chromosomes of E. coli and of other bacteria are single closed circles. Circular DNA molecules are also found in mitochondria, chloroplasts, and many viruses. Further complexity arises from the fact that the circles of DNA are sometimes interlocked in chainlike fashion (catenated). An unusual example of this phenomenon is the presence of thousands of small catenated DNA circles in the single mitochondrion of a trypanosome (Fig. 5-16).183 Sometimes circular DNA is knotted as in Fig. 5-17.184-186 Knots and catenanes often appear as intermediate forms during replication and recombination, especially involving circular DNA.187 188... 

Figure 5-16 (A) Electron micrograph of the network of catenated DNA circles in the mitochondrion of the trypanosome Crithidia fasciculata. (B) and (C) The same network after treatment with a topoisomerase from bacteriophage T4 that catalyzes a decatenation to form individual covalently closed circles (Chapter 27). Five times as much enzyme was added in (C) as in (B). Two sizes of circles are present. Most are "minicircles", each containing about 2300 bp but a smaller number of larger 35-kb "maxicircles" are also present. One of these is marked by the arrow. From Marini, Miller, and Englund.183...

Mitochondria are present in all eukaryotic cells that use oxygen in respiration, but the number per cell and the form and size vary.1-4 Certain tiny trypanosomes have just one mitochondrion but some oocytes have as many as 3 x 105. Mammalian cells typically contain several hundred mitochondria and liver cells5 more than 1000. Mammalian sperm cells may contain 50-75 mitochondria,6 but in some organisms only one very large helical mitochondrion, formed by the fusion of many individual mitochondria, wraps around the base of the tail. Typical mitochondria appear to be about the size of cells of E. coli. However, study of ultrathin serial sections of a single yeast cell by electron microscopy has shown that, under some growth conditions, all of the mitochondria are interconnected.7... 

Mitochondria are present in all eukaryotic cells that use oxygen in respiration, but the number per cell and the form and size vary. Certain tiny trypanosomes have just one mitochondrion but some oocytes have as many as 3 x 10 . Mammalian cells typically contain several himdred mitochondria and liver cells more than 1000. Mammalian sperm cells may contain... 

Giffin, B. F. and McCann, P. P. (1989) Physiological activation of the mitochondrion and the transformation capacity of DFMO induced intermediate and short stumpy bloodstream form trypanosomes. Am. J. Trop. Med. Hyg. 40, 487-493. 

Kinetoplast a structure at the base of the single flagellum of a trypanosome. The K. has a high affinity for basic dyes, and was first observed early in the 20th century by light microscopy. Electron microscopy shows that the K. is a disc-like structure in the matrix of the cell s single mitochondrion. The K. has attracted biochemical interest because it contains an unusual form of highly catenated DNA, known as kinetoplast DNA (kDNA). See Catenane. 

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