Three-card trick

Abstract

Abstract Bacterial cells are internally simple, while eukaryote cells are larger and assemble into organisms of all sizes. The eukaryote cell is a composite creature, assembled like Dr Frankenstein’s monster from the bolted-together body parts of at least two, maybe three, other single-celled organisms. The first eukaryotic cell came together about 1.8 billion years ago when a microbe belonging to a mysterious, little-known group called archaea ingested a bacterium that had a promising talent for generating energy. Ultimately, that symbiotic bacterium became an indispensable part of the eukaryote cell in the shape of the mitochondrion. Mitochondria are imprisoned in the cytoplasm, which means they are transmitted only down the female line when eukaryotes have sex. This narrow channel of transmission sealed their fate as subordinate partners in the symbiosis. Mitochondria still possess some of their own bacterial genes, but over time the most important ones were transferred to the nucleus, robbing mitochondria of their independence and sealing the major transition. As in every team, the parts may occasionally try to go their own way, causing mitochondrial malfunction and disease. It is difficult to overstate the importance of the major transition to the eukaryote cell because it made complex, multicellular life possible. When the first eukaryote cells married up with mitochondria, they acquired a generator, but that generator required an external source of fuel. Another acquisition added an independent source of fuel to the cell in a major transition in evolution that turned the world green.