its a description of the origin of eukaryotic cells and the interaction with prokayotes.

1. AUTHOR: SHAREEF NGUNGUNI
TITLE: ENDOSYMBIOTIC THEORY
INTRODUCTION
According to Margulis,(1970) it is a theory that tries to say about evolutionary origin of
today’s modern eukaryotic cells. It proposes that organelles that are found in eukaryotic cells,
more notably mitochondria, chloroplasts and others originated from endocytosis of aerobic
bacteria and cyanobacteria by anaerobic prokaryotic cells (archaeabacteria).Unable to digest
the engulfed bacteria over billions of years, they have developed a symbiotic relationship
that’s why the name endosymbiosis.The prokaryotes that failed to utilize oxygen begun to
acquire abilities to carry out aerobic respiration and eventually photosynthetic reactions by
successful endosymbiosis events. As time progressed, the engulfed bacteria transferred some
genes into the host cell’s genome resulting into permanent interdependence of each other
others metabolic activities.Eventually they developed into some of the known organelles such
as mitochondria and chloroplasts.
EVIDENCES THAT SUPPORT THE THEORY
Both mitochondria and chloroplasts have unique single, circular DNA that is not associated
with histone-proteins that are associated with wrapping of DNA in eukaryotes(Rodger and
John,1987).This indeed bears an extremely resemblance to prokaryotes which also bears its
own circular DNA free from histones
Mitochondrion has 70S ribosome that is found in prokaryotes but not in eukaryotes, and they
have their own protein synthesizing mechanism that relates to prokaryotes. Antibiotic such as
streptomycin block protein synthesis in bacteria (prokaryotes) but not in eukaryotes and they
too block protein in mitochondria.
EVIDENCES THAT OPPOSE THE THEORY
However this hypothesis does not explain the emergence of non-plastid organelles such as
endoplasmic reticulum, Golgi apparatus and the nucleus. These organelles evolved by
themselves in proto-eukaryotes (autogenesis hypothesis) and were not borrowed from other
organism by any symbiotic process (Margulis, 1970).
There are differences in structure between the membranes of bacteria and mitochondria. This
is evident as antibiotics are able to distinguish between the membranes of mitochondria and
bacteria. This difference in membrane structure argues against the idea that mitochondria
evolved from bacteria.

2. REFERENCES
 Margulis, L.,(1970). Origin of Eukaryotic Cells, Yale University Press.New York,USA.
 Nancy,C., Cynthia,Wr., Orna,C., Gisela,S., Carol,G., Rachel,G.,(2010). Molecular
Biology:Principles of Genome Function. Oxford University Press. New York,USA
 Rodger ,Y.S. and John ,L.I. (1987). General Microbiology.5th
Edition McMillan Education Ltd.
Londan, UK.