Mitochondria-Related Organelles in Protozoan Parasites
Many protozoans, including several protozoan parasites that cause infections in humans, can be identified
by their unusual appearance. Distinguishing features may include complex cell morphologies, the presence
of unique organelles, or the absence of common organelles. The protozoan parasitesGiardia lambliaand
Trichomonas vaginalisare two examples.
G. lamblia, a frequent cause of diarrhea in humans and many other animals, is an anaerobic parasite
that possesses two nuclei and several flagella. Its Golgi apparatus and endoplasmic reticulum are greatly
reduced, and it lacks mitochondria completely. However, it does have organelles known as mitosomes, double-
membrane-bound organelles that appear to be severely reduced mitochondria. This has led scientists to
believe thatG. lamblia’s ancestors once possessed mitochondria that evolved to become mitosomes.T.
vaginalis, which causes the sexually transmitted infection vaginitis, is another protozoan parasite that lacks
conventional mitochondria. Instead, it possesses hydrogenosomes, mitochondrial-related, double-membrane-
bound organelles that produce molecular hydrogen used in cellular metabolism. Scientists believe that
hydrogenosomes, like mitosomes, also evolved from mitochondria.[28]Plasma Membrane
The plasma membrane of eukaryotic cells is similar in structure to the prokaryotic plasma membrane in that it is
composed mainly of phospholipids forming a bilayer with embedded peripheral and integral proteins (Figure 3.52).
These membrane components move within the plane of the membrane according to the fluid mosaic model. However,
unlike the prokaryotic membrane, eukaryotic membranes contain sterols, including cholesterol, that alter membrane
fluidity. Additionally, many eukaryotic cells contain some specialized lipids, including sphingolipids, which are
thought to play a role in maintaining membrane stability as well as being involved in signal transduction pathways
and cell-to-cell communication.
Micro Connections
- N. Yarlett, J.H.P. Hackstein. “Hydrogenosomes: One Organelle, Multiple Origins.”BioScience55 no. 8 (2005):657–658.
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