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The theory of endosymbiosis

Extracts from this essay...

Introduction

The theory of endosymbiosis (Endo Within, Symbiosis Living together! ) I am going to analyze the theory of endosymbiosis over the next few pages. I am going to give arguments for and against so I can make a reliable conclusion. First of all I am going to give some information about the theory of endosymbiosis. According to the theory of endosymbiosis, billions of years ago mitochondria and chloroplasts were free-living bacteria (prokaryotes) which somehow became part of an early cell. The primitive Earth did not have oxygen in its atmosphere so these early cells must have been able to survive with out oxygen. However, oxygen gradually oxygen built up in the atmosphere and it is possible that some bacteria evolved which were able to use oxygen for respiration (aerobic bacteria). According to the theory, an aerobic bacterium became engulfed by an anarobic amoeba-like bacterium, and the amoeba-like bacterium navigated through the newly oxygen rich waters in search of food. In support of this theory of endosymbiosis, scientists have shown that oxygen began to accumulate between the first fossil records of prokaryotes and the later fossil records of eukaryotes. Anaerobic amoeba-like Anerobic bacterium Aerobic bacterium bacterium. engulfs aerobic bacterium. becomes symbiotic inside the anarobic bacterium.

Middle

Arguments for the theory of endosymbiosis. In 1960 a scientist called Lynn Margullis came up with a theory of endosybiosis. She said that if the theory of endosymbiosis was true the mitochondria and chloroplasts would have there own DNA because they come from different places and is unable to be produced by the other part of the symbiotic cell. In the 1980s it was found out that these organelles do indeed have their own DNA. Also like bacteria they have there own singular circular piece of DNA without any proteins attached. A main argument for the theory of endosymbiosis is that we know mitochondria and chloroplasts can only be formed from pre-existing mitochondria and chloroplasts. They cannot be formed in a cell which lacks these organelles because nuclear genes code for only some of the proteins of which they are made. Both mitochondria and chloroplasts have their own protein-synthesizing machinery, which resembles that of prokaryotes, but these are smaller than (70s) type found in bacteria, not the larger kind found in eukaryotic cells. Strong evidence favors Margulis's theory. There are plenty of examples of nature continuing to tinker with endosymbionts, the mitochondria are like bacteria in size and structure. The inner mitochondrial membrane is like a bacterial plasma membrane.

Conclusion

There are other theories to explain the evolution of eukaryotic cells. One argument is that mitochondria and chloroplasts can produce only a few proteins. Most of the enzymes found in the organelles are coded for by the nuclear DNA. Supporters of the endosymbiotic theory suggest that some organelle DNA "jumped" to the nuclear DNA during evolution. This is why neither chloroplasts or mitochondria are able to live independently of the eukaryotic cell. Some people belive that mitochondria and chloroplasts developed by some kind of "pinching off" of the cell membrane. Others belive that some early bacteria developed a "casing" around them selves, which is what we now call a eukaryotic cell. Conclusion I conclude that the theory of endosybiosis has enough evidence to show that it is true. Although we can't be 100 percent sure that this is the was it occured. I think that Lynne Margullis' theory is pretty conclusive as the cell cant reproduce a different set of DNA also the mitochondria and chloroplasts cannot be reproduced unless its by pre existing mitochondria and chloroplasts. This shows that the cell cannot produce these organelles making it pretty safe to assume that these two cells are symbiotic. So the strength of this evidence leads me to belive that the theory is true but I'm not going to say that is for sure the case as there is no solid evidence that proves this to be the case.

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