Which of the following is the strongest evidence supporting the endosymbiont hypothesis?
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Mitochondria theory
Mitochondria in vitro
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Evolutionary Origin of MitochondriaUnlike any other organelle, except for chloroplasts, mitochondria appear to originate only from other mitochondria. They contain their own DNA, which is circular as is true with bacteria, along with their own transcriptional and translational machinery. Mitochondrial ribosomes and transfer RNA molecules are similar to those of bacteria, as are components of their membrane.These and related observations led Dr. Lynn Margulis, in the 1970s, to propose an extracellular origin for mitochondria.Some species of present day protists contain living organisms within their cytoplasm. For example, Paramecium bursaria are hosts for zoochlorellae, photosynthetic protists, that reside within the cytoplasm. The relationship appears to be symbiotic. The endosymbiont gains protection and possibly some essential nutrients from the host cytoplasm. The host has a readily available food source when its usual food source is depleted. If you have the opportunity to observe P. bursaria, note that the endosymbionts are not incorporated into food vacuoles. They are residents within the cytoplasm itself, and either are descended from organisms that survived endocytosis or have some mechanism for escaping food vacuoles once they are ingested. Protists are eukaryotes, of course, meaning that their genetic material is organized into a compartment, the nucleus, that is surrounded by membrane, and that they have membrane-delineated organelles. In the warm seas of the ancient earth, the first living things would have been prokaryotes. The endosymbiotic hypothesis for the origin of mitochondria (and chloroplasts) suggests that mitochondria are descended from specialized bacteria (probably purple nonsulfur bacteria) that somehow survived endocytosis by another species of prokaryote or some other cell type, and became incorporated into the cytoplasm. The ability of symbiont bacteria to conduct cellular respiration in host cells that relied on glycosis and fermentation would have provided a considerable evolutionary advantage. Similarly, host cells with symbiont bacteria capable of photosynthesis would also have an advantage. In both cases, the number of environments in which the cells could survive would have been greatly expanded. Mitochondria do not contain anywhere near the amount of DNA needed to code for all mitochondria-specific proteins, however, a billion or so years of evolution could account for a progressive loss of independence. The endosymbiotic hypothesis might be called a theory, but experimental evidence can't be provided to test it. Only circumstantial evidence is available in support of the proposal, which is the most likely explanation for the origin of mitochondria. The evidence needed to change the model from hypothesis to theory is likely forever lost in antiquity. Understanding: • The origin of eukaryotic cells can be explained by the endosymbiotic theory Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell (e.g. photosynthesis) Over generations, the engulfed cell lost some of its independent utility and became a supplemental organelle Overview of the Process of Endosymbiosis Evidence for Endosymbiosis Mitochondria and chloroplasts are both organelles suggested to have arisen via endosymbiosis Evidence that supports the extracellular origins of these organelles can be seen by looking at certain key features:
Chloroplast and Mitochondrial Evidence What is the strongest evidence in support of the endosymbiotic theory?Protein import is the strongest evidence we have for the single origin of chloroplasts and mitochondria. It is probably also the strongest evidence we have to sort out the number and nature of secondary endosymbiotic events that have occurred in evolution involving the red plastid lineage.
What is the evidence for the Endosymbiotic hypothesis?In addition to the lack of histones, mitochondria and chloroplasts have circular, single stranded DNA. Single stranded, circular DNA is found exclusively in prokaryotes. This evidence supports the endosymbiosis theory because these characteristics would allow the mitochondria and chloroplasts to survive on their own.
What are 3 sources of evidence for the endosymbiont theory?Evidence for Endosymbiosis
Evidence that supports the extracellular origins of these organelles can be seen by looking at certain key features: Membranes (double membrane bound) Antibiotics (susceptibility) Division (mode of replication)
What are 5 pieces of evidence that support the Endosymbiotic hypothesis?10 Evidence of endosymbiotic theory:. i) Presence of DNA:. ii) Size of Ribosomes:. iii) Inhibition by antibiotics:. iv) Evolutionary relationship:. v) Same size:. vi) Plasma-Membrane:. vii) Enzyme secretion:. viii) Replication and protein synthesis:. |
