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DA6. Diversity of Life

Statement

In your assigned readings, you learned about different theories for the evolution of eukaryotic cells from prokaryotic organisms. Describe the hypothesized steps for the evolution of eukaryotic cells via endosymbiosis. How is evidence used to support this theory? Explain your position.

Solution

The living world is divided into two groups: Prokaryotes (Archaea and Bacteria) and Eukaryotes. The endosymbiotic theory suggests that eukaryotes evolved from prokaryotes, two prokaryotes cells (probably archea and bactera) fused together to form the common ancestor of eukaryotes (Rye et al., 2016, p. 600).

endosymbiosis explains a cell that went inside another host cell (engulfing) such that both cells live (cell lives inside the host cell); with time, a symbiotic relationship is formed between the two cells, such that each cell benefits from the other. And with even more time, the engulfed cell becomes an organelle inside the host cell (Rye et al., 2016, p. 601).

The endosymbiotic theory suggests that mitochondria and chloroplasts were once free-living prokaryotes that were engulfed by larger prokaryotic cells (Rye et al., 2016, p. 601).

The similarities between mitochondria and chloroplasts, and their differences from other parts of the cell support their external origin, especially that they have their own circular DNA and ribosomes, the double membrane, the way they reproduce, and their aerobic respiration (Rye et al., 2016).

The mitochondria and chloroplasts genes that are responsible for replication appears closer to those in Archaea, while the genes responsible for energy-harvesting processes had their origins in bacteria (Rye et al., 2016, p. 601).

Most mitochondria are shaped like alpha-proteobacteria and are surrounded by two membranes which suggests that one is the original membrane of the engulfed cell and the other is a membrane is generated by the host cell, especially as mitochondria cannot survive outside the cell (Rye et al., 2016, p. 602).

The mitochondrial inner membrane is folded in away that matches outer membrane of alpha-proteobacteria, and the membrane and the matrix are rich with the enzymes necessary for aerobic respiration (Rye et al., 2016, p. 602).

mitochondria are not formed from scratch by the eukaryotic cell; they reproduce within it and are distributed with the cytoplasm when a cell divides or two cells fuse, and their reproduction is synchronized with the activity and division of the cell (Rye et al., 2016, p. 602).

The previous features of mitochondria and chloroplasts supports their endosymbiotic origin, and the theory is widely accepted by the scientific community, but further research may disclose more interesting features(Rye et al., 2016).

References