Cynthia Hibbs-Hussain
Biology II
Week 1 Narrative
The Origin Of Multicellular Life
The theory of evolution presented by Charles Darwin, supports that natural selection, over time could through mutation of already established organisms lead to the development of new species. This theory in itself did not answer the question of how multicellular organisms came to be. While DNA was identified in 1869, it was not until 1953 that James Watson and Francis Crick actually determined the molecular structure of DNA. In the late 1960's, Lynn Margulis chose to study DNA outside of the nucleus when she observed two of her professor's discover it in chloroplasts. It was from here she developed the theory of endosymbiosis in the evolution of prokaryote cells to eukaryote cells.
The physical similarity between bacteria and mitochondria is apparent. It was suggested that mitochondria began from bacteria that lived in symbiosis within the cells of plants and animals, as well as the chloroplasts of plants. These observations lead to the hypothesis that the bridge between unicellular organisms and multicellular organisms was a result of endosymbiosis. This was not a new concept, but the evidence was not in place to support it. The serial endosymbiosis theory (SET) states that the evolution of eukaryotes from prokaryotes involved more than one symbiotic union of previously independent ancestors. These were a host cell, ancestral mitochondria, or ancestral chloroplasts and a prokaryote cell that contributed structures to provide cellular motion.
In simple terms, when symbiosis occurred, two distinct cells were present within the same cellular wall. In the case of the eukaryotic animal cell, the symbiot developed into the mitochondria, which is responsible for energy production. In plants, it became the chloroplast.
During the development of many of her theories, scientists discovered the mechanism of symbiotic relationships...