Evidence for Endosymbiotic Theory

Topics: Bacteria, Organelle, Cell Pages: 4 (1321 words) Published: October 9, 2012
Evidence for Endosymbiotic theory:

Evidence that mitochondria and plastids arose from bacteria is as follows:[13][14][15] * New mitochondria and plastids are formed only through a process similar to binary fission. * In some algae, such as Euglena, the plastids can be destroyed by certain chemicals or prolonged absence of light without otherwise affecting the cell. In such a case, the plastids will not regenerate. This shows that the plastid regeneration relies on an extracellular source, such as from cell division or endosymbiosis. * They are surrounded by two or more membranes, and the innermost of these shows differences in composition from the other membranes of the cell. They are composed of a peptidoglycan cell wall characteristic of a bacterial cell. * Both mitochondria and plastids contain DNA that is different from that of the cell nucleus and that is similar to that of bacteria (both in their size and their having a circular form). * DNA sequence analysis and phylogenetic estimates suggest that nuclear DNA contains genes that probably came from plastids. * These organelles' ribosomes are like those found in bacteria (70S). * Proteins of organelle origin, like those of bacteria, use N-formylmethionine as the initiating amino acid. * Much of the internal structure and biochemistry of plastids, for instance the presence of thylakoids and particular chlorophylls, is very similar to that of cyanobacteria. Phylogenetic estimates constructed with bacteria, plastids, and eukaryotic genomes also suggest that plastids are most closely related to cyanobacteria. * Mitochondria have several enzymes and transport systems similar to those of bacteria. * Some proteins encoded in the nucleus are transported to the organelle, and both mitochondria and plastids have small genomes compared to bacteria. This is consistent with an increased...
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