I stated in my last post that it would be impossible for bacteria to evolve eukaryote-like complexity without symbiosis because trim genomes and small size are selected for. The size of bacteria is constrained because they need a high surface area to volume ratio in order to respire. But, some bacteria have found ways to increase surface area by changing shape or with infolded membranes. We know that this path has never led to complexity over 4 billion years of evolution, but why?
Lane believes that it is because as energy generation becomes larger and more complex, local control is essential. We all know that mitochondria have their own genome. Over time, mitochondrial genes have migrated to the nucleus. The exact genes that have migrated are different in different species but there is no species that has lost all mitochondrial genes. The ones that are retained generally benefit local energy production regulation. There are many disadvantages to retaining genes in the mitochondria. They evolve about 20 times faster than nuclear genes as they are more susceptible to mutation. Also, the genetic machinery must be maintained in each of the hundreds of mitochondria in each cell. Since we know that there is not even 1 example of a eukaryote losing all of its mitochondrial genes, there must be a huge advantage to these genetic outposts. Lane argues that local control is absolutely essential. If mitochondria didn't have their own genomes, they would not be able to individually regulate energy production. Regulating hundreds of mitochondria from the nucleus would be extremely complex and it may not be possible for such a mechanism to evolve. This is the problem with bacteria with infolded membranes. If they were to grow and become more complex, localized control of energy production would be essential but there is no mechanism for such a structure to evolve. Symbiosis got around this problem. That is why eukaryotes alone broke free of their bacterial chains!
No comments:
Post a Comment