As they became more interdependent an obligatory symbiosis evolved." (Margulis, Live Chat, n.p.)
The Theory of Endosymbiosis also states that eukaryotic undulipodia originated from spirochete bacteria. The term "undulipodia" is used to describe the eukaryotic motility organelles, flagella and cilia. Undulipodia are composed of microtubules in a specific configuration. Microtubules are comprised of several closely related proteins called tubulins. These structures are far larger and more complex than bacterial flagella, which are made of flagellin proteins. The Endosymbiosis Theory postulates that undulipodia may be derived from bacteria through motility symbioses. This idea is referred to as the exogenous hypothesis. The series of explanations that lead up to the detailed elaboration of the endobiotic origins of the flagellum and cilia point to several lines of circumstantial evidence. The argument emphasizes the biology of the organelles themselves, their distribution, and the occurrence of related and analogous structures.
The Theory of Endosymbiosis significantly stimulated a variety of analytic approaches to the problem of organelle origins. Support for the endobiotic origin of mitochondria and chloroplast is very strong. Margulis included in her theory the proposition that the eukaryotic flagellum evolved from an endosymbiotic spirochete like prokaryote that became part of its eukaryotic protistan host. The major line of information in this regard has come from her studies of an unusual group of spirochetes that live on and in protists. These spiral bacteria depend for their locomotion on bundles of typical bacterial flagella, but some also have microtubules, which are not found in other prokaryotes but are ubiquitous in eukaryotic cells.(Avers, 124)
There is a substantial amount of evidence within the theory itself to suggest that such a postulation of evolution of the eukaryotic cell is correct, with regard to the origins of mitochondria and chloroplasts. Much of this evidence is based on the differing features of the two types of cells, and similarities between mitochondria and chloroplasts and present day prokaryotes, the bacteria. The considerable substantiations, as elaborated above seem to indicate that the theory of serial endosymbiosis is correct. One such fact is that previously non-existing mitochondria or chloroplasts, if required to be freshly produced, cannot be synthesized in the body without the presence of an original organelle. The reason for this is that the nucleus inside the cell, which contains the genetic code for the rest of the cell, encoded onto DNA molecules, does not contain sufficient coding to account for all of the proteins present in the organelles. There are some proteins present in the organelles which are missing altogether in the DNA code of the nucleus and there are some which differ slightly from those present inside the nucleus. The "missing" DNA is accounted for by the loop of DNA present inside the organelle. This DNA is of the same form as is present in all prokaryotic cells. That is, the DNA is circular, and it lies free in the "cytoplasm" of the