Evolution of the Cell

Before I begin, I want to say that I'm a evolutionist, even though I may be asking creationist questions. That's just because I am involved in a EvC debate on another board(any of you evolutionists are welcome to come a back me up )Anyway, the question was asked. How can evolution explain the processes such as the Kreb Cycle and the organelles?Any help would be appreciated

Which particular organelles were you thinking of? Mitochondria and chloroplast are now generally held to have become part of the eukaryotic cell by a process termed endosymbiosis. This involves one unicelluar organism, the proto-eukaryote, engulfing a smaller unicellular organism, these have been speculated be a related to the purple bacteria or cyanobacteria. These endocytosed bacteria, and their intracellular progeny, develop a symbiotic relationship with the host cell and over time (many generations) lose their independence and become obligate endosymbionts, neither the host cell nor the endosymbiont can exist independently.This is an unusual example and clearly the initial endocytic event doesn't fit into the normal way of gradualistic evolution by genetic change, although the subsequent exchange and loss of genetic material arguably do. Having said this evidence suggests that mitochondria are the result of a single event while chloroplasts may have developed twice, showing that endosymbiosis is by no means a unique event.Lynn Margulis, the originator of the Serial Endosymbiont Hypothesis, suggests that the modern eukaryotic cell is the result of a series of endosymbiotic events and proposed that the nucleus, the flagellae and various other organelles were also products of endosymbiosis. At the moment plastids and mitochondria are the only generally accepted examples of common organelles thought to have originated through endosymbiosis, there are some less common ones as well but they are not particularly relevant.[This message has been edited by Wounded King, 09-15-2003]

That's exactly the type of answer I was looking for, thanks That also helps explain processes such as the Kreb Cycle and Photosynthesis.

Could you explain how a proto-eukaryotic cell could divide without the organelles' information in its DNA?Thanks a lot.[This message has been edited by MonarchzMan, 09-14-2003]

Just like a prokaryote...Prokaryotes have no organelles. Archeae and bacteria fall into this category.Oh, and there are no organelles in DNA. Some organelles do contain DNA however.------------------
No webpage found at provided URL: www.hells-handmaiden.com[This message has been edited by John, 09-13-2003]

There isn't any organelle information in DNA? Pardon my ignorance, but how can a cell divide nd have the correct organelles if there isn't any DNA to code for them?I do know that mitochondira have DNA and ribosomes are made up of rRNA, but I didn't realize that other organelles, like chloroplast and the ER weren't coded for in the DNA.Could you go into more depth about how that happens? I didn't cover that much about cell division in biology, so all the help is appreciated

Picture that clusters of protolife initially were like a soup of all kinds of materials, each type encouraging the formation of others like them from the energy source (such as a hydrothermal vent). In such a case, the first cell membrane could just enclose a collection of these different chemicals - not all that different from a modern prokaryote. Of course, it would eventually use up its energy source that it previously used to replicate. *However*, it would also be protected by the membrane from damage, and thus would be dormant like a spore - which could be a great advantage in a number of cases.How would such a cell membrane form? That's the easy part Phospholipds inherently form into bilayer sheets. When disturbed, they form "bubbles" of varying sizes.------------------
"Illuminant light,
illuminate me."

How would organelles replicate if the DNA to make those organelles was absent from the host cell's DNA?

I would presume that the ones with their own DNA or RNA, like mitochondria, use their own DNA to replicate. Similarly other organelles may catalyze their own replication, or are simple enough that all they have to do is divide. I imagine ER or Golgi bodies are like that, but I'm no biologist.

The chloroplasts have their own separate genome just like the mitochondria.In both cases, a large number of genes for organellar function have been taken over by the nucleus. We see that there is a huge amount of DNA traficing over time between the organelles and the nuclear genome in the form of nuclear mitochondrial DNA insertions or NUMTS. Same goes for chlorplasts.

I think this has been said piecemeal, but to summarise.In the proto-eukaryote, after the initial endocytic event, the proto-mitochondria replicates within the host cell as it would normally outside and has its own genome. The protoeukaryote replicates normally but the proto-mitochondria living in the cytoplasm are inherited by both daughter cells when the cytoplasm is divided between them.Over time various elements of the mitochondrial DNA have been integrated into the nuclear DNA and lost from the mitochondrial DNA so that the nuclear contained DNA is now required for mitochondria to be produced, which is one reason why they are now obligate endosymbionts.

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There isn't any organelle information in DNA?

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This is not what you said. Your statement was there were organelles in DNA, not code in the DNA to produce the organelles. Organelles have there own DNA, however, they can't function without the nuclear DNA, which has taken on much of what the organelle's DNA used to do.Weren't you originally asking how a pre-eukaryotic cell could function? If so, you only have to look to the prokaryotic archaea and bacteria. The nutshell version of eukaryote emergence is that prokaryotic cells ate other prokaryotic cells and that some of these consumed cells managed to survive-- much like parasites today manage to survive the body's defenses. The cells conferred mutual advantage and the union was perpetuated. Viola-- eukaryote! There are very strong cases for this as the origin of a couple of different organelles-- mitochondria and chloroplast--, but that all or most originated similarly is not unreasonable.------------------
No webpage found at provided URL: www.hells-handmaiden.com

Sorry for the confusion, John.Thank you for the information all! Though, I don't think that the creationists will like this answer as they don't like me saying that it happened over time. They just don't realize that you can't talk evolution without the great time it involves..