Читать книгу Algorithms in Bioinformatics - Paul A. Gagniuc - Страница 63

Chloroplasts were once free-living cyanobacteria, while mitochondria were once free-living proteobacteria. Both have preserved remnants of eubacterial genomes. The average genome size of eukaryotic organelles was calculated at 0.07 Mb (70 kb). With a few exceptions, the average values from each type of organelle show a uniformity regarding the genome size (Table 2.3). Assuming a somewhat constant reductive evolution, this observation may indicate the occurrence of primary and secondary endosymbiosis during the same period for most of the organelles.

Depending on the species, both chloroplasts and mitochondria have evolved slightly differently, however, sometimes even radically different by accelerated reductive evolution (e.g. hydrogenosomes). Many known membrane-bound organelles are derived from either cyanobacteria or proteobacteria lineages. Nonetheless, there are organelles that show a more recent history, different from that of chloroplasts or mitochondria. One such organelle is the chromatophore. About chromatophores and other plastid-like or mitochondria-like organelles, we will discuss further. However, discussions will include only the organelles currently considered by the NCBI database. Note that there are other variations of DNA-containing organelles that have been cataloged as “other plastids” and others who are just waiting to be discovered.