trans

C H A P T E R
12
Plastids, mitochondria, and
hydrogenosomes
Geoffrey Ian McFadden
School of Botany, University of Melbourne, Victoria, Australia
INTRODUCTION
One of the key differences between eukaryotes
and prokaryotes is the numerous subcellular
compartments present in eukaryotic cells. In
addition to the nucleus, eukaryotes possess
compartments such as the endomembrane
system, mitochondria, and in some cases plastids.
None of these compartments occurs in
prokaryotes. Indeed it is the presence of these
compartments and the ability to compartmentalize
processes that has allowed eukaryotic
cells to expand in size and, more importantly,
to differentiate into various cell types, each
with a unique role, in a multicellular consortium.
It is reasonably certain that prokaryotes
preceded eukaryotes in the evolution of life on
earth. Therefore, the simple prokaryotic cellular
organization is considered ancestral to the
more complex, compartmentalized eukaryotic
cell organization. This chapter examines the
origin of two eukaryotic compartments, the
mitochondrion and plastid, their significance
in the evolution of parasites, and the role of
these organelles in treatment of several parasitic
diseases.
ENDOSYMBIOSIS
The theory of endosymbiosis describes the
origin of mitochondria and plastids from
endosymbiotic bacteria. The theory is an old
one, going back to early studies by light microscopists
in the late 1800s, and has gained more
and more support as the details of the inner
workings of these organelles have emerged
with the advent of new technologies such as
biochemistry, electron microscopy and molecular
biology. Indeed, as the evidence accumulates
we are increasingly more certain that
mitochondria and plastids are relics of once
free-living prokaryotes now housed within
eukaryotic cells. What are the main lines of evidence
for this assertion? Firstly, these organelles
are what is known as semi-autonomous. That
Molecular Medical Parasitology
ISBN 0–12–473346–8
277
Copyright © 2003 Elsevier Science Ltd.
All rights of reproduction in any form reserved.