Cells and Molecules - Brutes or Angels: Human Possibility in the Age of Biotechnology - page 25

fig. 1.11. The endosymbiotic origin of mitochondria. A small prokaryotic cell with
a circular chromosomal DnA and ATP-producing enzymes in its outer membrane
established an obligatory endosymbiotic relationship with a larger prokaryotic cell that
lacked an ATP-producing membrane. engulfment of the smaller cell gave the larger cell
an additional, host-derived membrane that became the outer membrane of modern-day
mitochondria.
how eukaryotic cells originated is better understood than exactly when
they first appeared. There is widespread agreement among molecular biolo-
gists, microbiologists, and cell biologists that eukaryotic cells arose when
some small prokaryotic cells took up permanent residence inside a larger
pre-eukaryotic cell. When one cell lives inside another cell, the relation-
ship is called endosymbiosis, symbiosis being the living together of two dif-
ferent organisms in a mutually beneficial association. An endosymbiotic
model for the origin of eukaryotic cells was proposed in 1970 by lynn
margulis. Today margulis's model enjoys overwhelming supportive evi-