Download Endosymbiosis: Eukaryotes and their Organelles

Endosymbiosis: Eukaryotes and their Organelles
If endosymbiosis never occurred, life as we know it would not exist.
Endosymbiosis is the process by which a few of the very important double
membrane organelles became a part of the formerly prokaryotic cells, namely the
mitochondria, chloroplast, and nucleus (Gray, 1989; Martin, 2005). You are
forgetting your audience. Remember, this is for a general reader. Try to imagine
yourself in their shoes. Would they understand this? You need to start general with
cells and their functions and then narrow in on how they perform these functions
using the so-called organelles. Use analogies or something. This will elucidate the
importance of the organelles and then you can get into origins. Organelles are the
structures located inside of a cell’s cytoplasm that help it to perform life functions.
The mitochondria helps a cell convert energy into a usable form, the chloroplast
helps green plants make food, and the nucleus stores a cell’s genetic information.
While most organisms have at least some organelles, there are distinct differences
between which ones prokaryotes and eukaryotes have. Prokaryotes, more
commonly known as bacteria, are simplistic, single-celled organisms that lack the
important membrane bound organelles, such as the nucleus, mitochondria,
chloroplast, etc. (Gojobori, Ikeo, & Ohyanagi, 2008). That’s where endosymbiosis
comes in. As primitive prokaryotic cells evolved into more complex eukaryotic cells,
they gained more organelles to help them carry out life functions more efficiently. It
is widely accepted that these organelles-which ones? Not all organelles… originated
from bacteria, but there are different theories on how exactly they were integrated
into the cell.
The big endosymbiosis mystery standing today is what exactly is the origin of
organelles?-is this first sentence necessary? A theory that attempts to answer this
question is the endosymbiotic theory.-didn’t you already mention this? The word
endosymbiosis is just a combination of “endo”, meaning to join with, and
“symbiosis”, the interaction between two different organisms living in close physical
association, typically to the advantage of both.-not really, that would be a type of
symbiosis (mutualism) It is universally accepted that the earlier organelles were
bacteria that were ingested into the cell, forming the first organelles. Different
organelles, it seems, have different bacterial origins. Research on the nucleus shows
that it is of an archaeal bacteria origin, meaning the type of bacteria ingested by the
cell that incorporated it was an archaea bacterium, a more primitive type of
bacterium more primitive than what? (Gojobori, Ikeo, & Ohyanagi, 2008). The two
similar organelles that are the chloroplast and mitochondria however, show
evidence that they are of eubacterial origin (just the normal, everyday bacteria you
know and love), but evolving on different branches at different times (Gray, 1989).There is no way the general reader will understand this. You need to get some data
in here. Up to this point you have given no evidence. The intro should discuss the
cell and the organelles and then transition into the endosymbiotic theory. The first
body paragraph needs to start getting into the evidence for the theory. This
speculation is supported also by research done to analyze prokaryotic and
eukaryotic genes.-you need to explain. What is the rationale? The data collected
supports the idea that two separate endosymbiotic events occurred: “one
premitochondrial (2.7 billion years ago,) and a later mitochondrial event (1.8 billion
years ago)” (Hedges et al., 2001).-say what? This, however, contradicts another
study that supports the idea that the mitochondria was the first endosymbiotic
event, but it did not significantly precede endosymbiosis of, say, the nucleus (Brown,
Chihade, de Pouplana, & Schimmel, 2000). There may have even been a third
endosymbiotic event occurring that incorporated the chloroplast into the cell, later
than the mitochondria, but also of a eubacterial origin (Gray, 1989). The data
collected and/or shown in different papers seem to agree that there was more than
one endosymbiotic event, but it seems that they still show uncertainty in exactly
how and when each event happened.-remember your audience. You need to simplify
and clarify.
Different ideas have been suggested to explain how some organelles came
into eukaryotic cells. For the nucleus, the most commonly accepted idea for its
origin is that the endomembrane system, which includes organelles such as the
nucleus and endoplasmic reticulum (ER), came about by a prokaryote taken into the
cell and being turned inside out so it forms a cavity. Another possible explanation is
that the symbiosis between a spirochete, a type or bacteria, and a type of wall-less
archaea bacteria. There are problems with this theory, though, as no evidence found
in the genome of the archaea bacteria that shows it has any relation to eukaryotes
(Martin, 2005). All these ideas support that the nucleus is derived from archaea
bacteria, with all endosymbiotic ideas relating to the nucleus involving archaea
(Fedorov, & Hartman, 2001; Martin, 2001; Gray, 1989). There are also different
ideas on the origin of the mitochondria and chloroplast. Research has shown
evidence that these organelles came into the cell at different times from each other
and from the nucleus. The chloroplast is an interesting organelle, as it has been
proposed that there may have been multiple origins of the chloroplast. Different
major groups of organisms that need them for photosynthesis, such as algae and
plants may have obtained them at separate times. The idea is that there were three
different endosymbiotic events in the history of chloroplasts (Gray, 2001). The
mitochondria is yet another organelle with an endosymbiotic origin. One question
that could be asked is, “Like chloroplasts, does the mitochondria have multiple
origins?” According to Michael Gray (2001), although mitochondria have an extreme
variation in size and organization, genetic information supports that it only has one
origin, so the answer to the question is “no.” I feel like you keep revisiting the same
story of these endosymbiotic events. The past two paragraphs seem to be discussing
the same idea, cells engulfing other cells. What is the difference? Make it clear.
Exactly how organelles became, well, organelles is one of the great mysteries
of cell biology.-say what? We-no personal pronouns do not know exactly how
everything happened, but we do have a lot of information and have begun to piece
together this great puzzle.-vague and informationless We do know that the nucleus
in all eukaryotic cells: from the trillions of cells in your body, to that annoying
mosquito trying to bite you, even down to that little amoeba you can’t even see,
originated from the endosymbiosis of an archaea bacteria (Olsen, Oyaizu, Oyaizu,
Yang, & Woese, 1985).-we know this? For sure? While the chloroplast and
mitochondria may seem so similar in function, they both convert energy, they both
have similar electron transport chains to make ATP, they actually came about
completely separately. Not only that, they came from different bacteria, at different
times. From purple photosynthetic bacteria, the mitochondria preceded the
chloroplast. It is actually a little bit ironic that it is the mitochondria that came from
photosynthetic bacteria, and not the chloroplast, which is used in photosynthesis of
plants. The chloroplast came from blue-green algae, another type of bacteria, and is
suggested to have 3 SEPARATE endosymbiotic events (Gray, 2001). The mystery of
how organelles came about is still unknown in detail to us, but we are getting closer
and closer to the truth. This conclusion is just a repeat of what you said above.
Basically, you continuously repeat that cells engulfed cells. Try getting into some of
the experiments that show this and forget about the details of how many times and
what came before what. Remember you audience. Get your point across. I will email
this to my mother and she should walk away understand something.
Put the references in alphabetical order, and I only count 6. Also, check the
formatting.
The number below will change with each revision. These numbers are simply indicative
of the amount of improvement required at this point. When you receive a 9 or greater,
the review is ready. DrT
6.5/10
References
William, M. (2005). Archae bacteria (Archaea) and the origin of the eukaryotic
nucleus, Science Direct 8:630-637.
Gray, M. W. (1989). The evolutionary origin of organelles, TIG, 5, 9.
Brown, J. R., Chihade, J.W., de Pouplana, L.R,. & Schimmel, P.R., (2000) Origin of
mitochondria in relation to evolutionary history of eukaryotic alanyl-tRNA
synthetase, PNAS, 97, 22, 12153-12157.
Gojobori, ,. Ikeo, K., & Ohyanagi, H.(2008). The origin of nucleus: Rebuild from the
prokaryotic ancestors of ribosome export factors. Gene, 423, 149-152.
Olsen, G.J., Oyaizu, Y., Oyaizu H., Yang, D., & Woese, C.R. (1985). Mitochondrial
Origins, PNAS, 82, 13, 4443-4447.
Blair Hedges, S., Chen, H., Kumar, S., Thompson, A.S., Y-C Wang, D., & Watanabe, H.
(2001). A genomic timescale for the origin of eukaryotes. BMC Evolutionary
Biology 2001, 1:4.
Fedorov, A, & Hartman, H.,(2001). The origin of the eukaryotic cell: A genomic
Investigation. PNAS, 99, 3, 1420-1425.
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