New Theory Suggests Alternate Path Led to Rise of the Eukaryotic Cell

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Newswise MADISON, Wis. As a fundamental unit of life, the cell is central to all of biology. Better understanding how complex cells evolved and work promises new revelations in areas as diverse as cancer research and developing new crop plants.

But deep thinking on how the eukaryotic cell came to be is astonishingly scant. Now, however, a bold new idea of how the eukaryotic cell and, by extension, all complex life came to be is giving scientists an opportunity to re-examine some of biologys key dogma.

All complex life including plants, animals and fungi is made up of eukaryotic cells, cells with a nucleus and other complex internal machinery used to perform the functions an organism needs to stay alive and healthy. Humans, for example, are composed of 220 different kinds of eukaryotic cells which, working in groups, control everything from thinking and locomotion to reproduction and immune defense.

Thus, the origin of the eukaryotic cell is considered one of the most critical evolutionary events in the history of life on Earth. Had it not occurred sometime between 1.6 and 2 billion years ago, our planet would be a far different place, populated entirely by prokaryotes, single-celled organisms such as bacteria and archaea.

For the most part, scientists agree that eukaryotic cells arose from a symbiotic relationship between bacteria and archaea. Archaea which are similar to bacteria but have many molecular differences and bacteria represent two of lifes three great domains. The third is represented by eukaryotes, organisms composed of the more complex eukaryotic cells.

Eukaryotic cells are characterized by an elaborate inner architecture. This includes, among other things, the cell nucleus, where genetic information in the form of DNA is housed within a double membrane; mitochondria, membrane-bound organelles, which provide the chemical energy a cell needs to function; and the endomembrane system, which is responsible for ferrying proteins and lipids about the cell.

Prevailing theory holds that eukaryotes came to be when a bacterium was swallowed by an archaeon. The engulfed bacterium, the theory holds, gave rise to mitochondria, whereas internalized pieces of the outer cell membrane of the archaeon formed the cells other internal compartments, including the nucleus and endomembrane system.

The current theory is widely accepted, but I would not say it is established since nobody seems to have seriously considered alternative explanations, explains David Baum, a University of Wisconsin-Madison professor of botany and evolutionary biologist who, with his cousin, University College London cell biologist Buzz Baum, has formulated a new theory for how eukaryotic cells evolved. Known as the inside-out theory of eukaryotic cell evolution, the alternative view of how complex life came to be was published recently (Oct. 28, 2014) in the open access journal BMC Biology.

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New Theory Suggests Alternate Path Led to Rise of the Eukaryotic Cell