Daily Archives: June 1, 2009

Front-loading mitochondria

In the past, I have provided multiple lines of evidence to establish the plausibility of front-loading evolution. However, we have focused primarily on the transition from a unicellular to a multicellular eukaryotic state. Let’s now take one step back and begin pondering whether eukaryotic cells were themselves front-loaded to appear. For without the eukaryotic cell design, it is unlikely that the planet would possess anything analogous to an animal or plant.

While we still don’t really understand the origin of the eukaryotic cell, there is a strong consensus about the origin of the mitochondria, a very important organelle of eukaryotes. According to the endosymbiotic theory, mitochondria are the descendents of bacteria. The theory postulates that a phagocytic cell engulfed some aerobic bacteria and rather than digest them, a symbiotic relationship was established, where each partner benefited from the new relationship. This relationship then set the stage for the ultimate stream-lining of the bacteria, such that they were transformed into mitochondria through the transfer of much of their gadgetry to the host nucleus.

In a nutshell, the essence of the argument for the endosymbiotic origin of mitochondria is that mitochondria look like they share a common ancestor with bacteria. The argument is quite convincing, as there are numerous mitochondrial genes whose sequences are much more similar to bacterial sequence than that which exists in the nucleus of the same cell. In fact, this is an example where no one piece of evidence carries the day, but instead it’s the cumulative power of multiple lines of evidence.

Since mitochondria were once bacteria, might this transition have been front-loaded to happen?

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