origin of eukaryotes

origin of eukaryotes - NEWSFOCUS On the Origin of...

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YOU MAY NOT FEEL AS THOUGH YOU HAVE much in common with a toadstool, but its cells and ours are strikingly similar. Animals and fungi both keep their DNA coiled up in a nucleus. Their genes are interspersed with chunks of DNA that cells have to edit out to make proteins. Those proteins are shuttled through a maze of membranes before they can float out into the cell. A cell in a toadstool, like your own cells, manufactures fuel in compartments called mitochondria. Both species’ cells contain the same molecular skeleton, which they can break down and reassemble in order to crawl. This same kind of cell is found in plants and algae; single-celled protozoans have the same layout as well. Other microbes, such as the gut bacterium Escherichia coli , lack it. All species with our arrangement are known as eukaryotes. The word is Greek for “true kernel,” referring to the nucleus. All other living things that lack a nucleus, mito- chondria, and the eukaryote LEGO-like skeleton are known as prokaryotes. “It’s the deepest divide in the living world,” says William Martin of the University of Düsseldorf in Germany. The evolution of the eukaryote cell is one of the most important transitions in the his- tory of life. “Without the origin of eukary- otes, we wouldn’t be here to discuss the ques- tion,” says T. Martin Embley of Newcastle University in the United Kingdom. Along with animals, eukaryotes gave rise to every other multicellular form of life. Indeed, when you look at the natural world, most of what you see are these “true kernel” organisms. The fossil record doesn’t tell us much about their origin. Paleontologists have found fossils of prokaryotes dating back 3.45 billion years. The earliest fossils that have been proposed to be eukaryotes— based on their larger size and eukaryotelike features on their surfaces—are only about 2 billion years old. Paleontologists have not yet discovered any transitional forms in the intervening 1.45 billion years, as they have for other groups, such as birds or whales. “One gets a bit of fossil envy,” says Anthony Poole of Stockholm University. Fortunately, living eukaryotes and prokaryotes still retain some clues to the transition, both in their cell biology and in their genomes. By studying both, researchers have made tremendous advances in the past 20 years in understanding how eukaryotes first emerged. A key step in their evolution, for example, was the acquisition of bacterial passengers, which eventually became the mitochondria of eukaryote cells. But some scientists now argue that the genes of these bac- teria also helped give rise to other important features of the eukary- ote cell, including the nucleus. “It’s been a really cool journey,”
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This note was uploaded on 08/30/2009 for the course BIO NA taught by Professor Stanger-hall during the Fall '09 term at UGA.

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origin of eukaryotes - NEWSFOCUS On the Origin of...

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