Endosymbiotic Theory

Certain organelles originated when free-living bacteria were taken into larger cells as endosymbionts.

…recall that all eukaryotic cells contain organelles. For example: nucleus mitochondria chloroplasts

How did organelles originate?

Endosymbiotic Theory proposed by some scientists from s. chloroplasts in plant cells resemble free-living cyanobacteria and proteobacteria.

The Cyanobacteria Eucapsis Photo by: Jason Oyadomari Chloroplasts (Elodea)

The proteobacteria Escherichia coli Mitochondrion

Endosymbiont endo (Gr.) “inside” syn (Gr.) = “with” biosis (Gr.) = “living”

Symbiosis close, often long-term interaction between different biological species.

Evidence New mitochondria and plastids are formed only through a process similar to binary fission. In some algae, such as Euglena, the plastids can be destroyed by certain chemicals or prolonged absence of light without otherwise affecting the cell. In such a case, the plastids will not regenerate. They are surrounded by two or more membranes, and the innermost of these shows differences in composition from the other membranes of the cell. They are composed of a peptidoglycan cell wall characteristic of a bacterial cell.

more evidence Both mitochondria and plastids contain DNA that is different from that of the cell nucleus and that is similar to that of bacteria (in being circular in shape and in its size). Much of the internal structure and biochemistry of plastids is very similar to that of cyanobacteria. Mitochondria have several enzymes and transport systems similar to those of bacteria. Mitochondria and plastids are similar in size to bacteria.

Vocabulary organelle cyanobacteria mitochondria plastid chloroplast eukaryote symbiosis phagocytosis

Resources McElroy, Kerensa Nature's best examples of symbiosis. Cosmos Magazine, Tuesday, 28 December 2010Cosmos Magazine, Tuesday, 28 December 2010