Diplomonads and Parabasalids

Two clades, the diplomon ads and the parabasalids, appear to represent the earliest surviving branches |EUKARYA in today's tree of eukary-otic life. It is likely that other clades diverged even earlier than the diplomonads and parabasalids. However, any such clades either were lost because of massive changes in the environment or remain hidden in rarely studied environments.

Diplomonads And Parabasalids

Common ancestor of all organisms

Protists Tree Life

28.9 Major Protist Groups in an Evolutionary Context All of the protist groups shown here, except certain green algae, appear to be clades.The protists themselves do not constitute a clade.We also show the prokaryotic domains and the plant, fungal, and animal kingdoms to provide context. The term "opisthokont" refers to organisms that have or had (ancestrally) a flagellum in a posterior position; this group includes a protist clade as well as the fungi and animals.

Both the diplomonads and the parabasalids are unicellular organisms that lack mitochondria. This absence of mitochondria may be a derived condition: Ancestors of these organisms may have possessed mitochondria that were lost in the course of evolution. The existence of such organisms to

(a) Diplomonad

(a) Diplomonad

Nuclei

Diplomonads

Nuclei

(b) Parabasalid

Posterior flagellum and undulating membrane

Posterior flagellum and undulating membrane

Anterior flagella

Diplomonads And Parabasalids

28.10 Two Protist Groups Lack Mitochondria Diplomonads and parabasalids appear to represent the most ancient surviving branches of eukaryotic life. (a) Giardia, a diplomonad, has flagella and two nuclei (see also Figure 28.1 b). (b) Trichomonas, a parabasalid, has flagella and undulating membranes. Neither of these protists possesses mitochondria.

Anterior flagella

28.10 Two Protist Groups Lack Mitochondria Diplomonads and parabasalids appear to represent the most ancient surviving branches of eukaryotic life. (a) Giardia, a diplomonad, has flagella and two nuclei (see also Figure 28.1 b). (b) Trichomonas, a parabasalid, has flagella and undulating membranes. Neither of these protists possesses mitochondria.

day shows that eukaryotic life is feasible without mitochondria, and for that reason, the diplomonads and parabasalids are the focus of much attention.

Giardia lamblia, a diplomonad, is a familiar parasite that contaminates water supplies and causes the intestinal disease giardiasis (Figure 28.10a). This tiny organism has no mitochondria, chloroplasts, or other membrane-enclosed organelles, but it contains two nuclei bounded by nuclear envelopes, and it has a cytoskeleton and multiple flagella.

Trichomonas vaginalis is a parabasalid responsible for a sexually transmitted disease in humans (Figure 28.10b). Infection of the male urethra, where it may occur without symptoms, is less common than infection of the vagina. In addition to flagella, the parabasalids have undulating membranes that also contribute to the cell's locomotion.

Euglenozoans

The euglenozoans are a clade of flagellates: unicellular organisms with flagella. They reproduce asexually by binary fission. There are two subgroups of euglenozoans: eugle-noids and kinetoplastids.

Euglenoids have anterior flagella

The euglenoids possess flagella arising from a pocket at the anterior end of the cell. Many members of the group are pho-

Pictures Euglenas
Photosynthetic chloroplasts are prominent features in a typical Euglena cell.

Pigment shield

Euglenoids Examples

Photoreceptor

Contractile vacuole

Stored polysaccharides from photosynthesis

28.11 A Photosynthetic Euglenoid Several Euglena species are among the best-known flagellates. In this species, the second flagellum is rudimentary.

Pigment shield

Photoreceptor

Contractile vacuole

Stored polysaccharides from photosynthesis

28.11 A Photosynthetic Euglenoid Several Euglena species are among the best-known flagellates. In this species, the second flagellum is rudimentary.

tosynthetic. Euglenoids used to be claimed by the zoologists as animals and by the botanists as plants.

Figure 28.11 depicts a cell of the genus Euglena. Like most other euglenoids, this common freshwater organism has a complex cell structure. It propels itself through the water with the longer of its two flagella, which may also serve as an anchor to hold the organism in place. The flagellum provides power by means of a wavy motion that spreads from base to tip. The second flagellum is often rudimentary.

Euglena has very flexible nutritional requirements. Many species are always heterotrophic. Other species are fully autotrophic in sunlight, using chloroplasts to synthesize organic compounds through photosynthesis. The chloroplasts of eu-glenas are surrounded by three membranes (unlike plant chloroplasts, which have only two; we will describe the history of the third membrane later in this chapter). When kept in the dark, these euglenas lose their photosynthetic pigment and begin to feed exclusively on dead organic material floating in the water around them. Such a "bleached" Euglena resynthesizes its photosynthetic pigment when it is returned to the light and becomes autotrophic again. But Euglena cells treated with certain antibiotics or mutagens lose their photosynthetic pigment completely; neither they nor their descendants are ever autotrophs again. However, those descendants function well as heterotrophs.

Kinetoplastids have mitochondria that edit their own RNA

The kinetoplastids are unicellular, parasitic flagellates with a single, large mitochondrion. That mitochondrion contains a kinetoplast—a unique structure housing multiple, circular DNA molecules and associated proteins. Some of these DNA molecules encode "guides" that edit RNA within the mitochondrion.

Undulating membrane

Undulating membrane

Euglenozoans

Trypanosoma gambiense

28.12 A Parasitic Kinetoplastid Trypanosomas, shown here among human red blood cells (round), cause sleeping sickness in mammals. A flagellum runs along one edge of the cell as part of a structure called the undulating membrane.

Trypanosoma gambiense

28.12 A Parasitic Kinetoplastid Trypanosomas, shown here among human red blood cells (round), cause sleeping sickness in mammals. A flagellum runs along one edge of the cell as part of a structure called the undulating membrane.

Some kinetoplastids are human pathogens. Sleeping sickness, one of the most dreaded diseases of Africa, is caused by the parasitic kinetoplastid Trypanosoma (Figure 28.12). An insect, the tsetse fly, is the vector (intermediate host) of Trypanosoma. Carrying its deadly cargo, the tsetse fly bites livestock, wild animals, and humans, infecting them with the parasite. Trypanosoma then multiplies in the mammalian bloodstream and produces toxins. When these parasites invade the nervous system, the neurological symptoms of sleeping sickness appear and are followed by death. Half a million people now have sleeping sickness, and 80 percent of them will die of the disease. About 3 million head of livestock die from Trypanosoma infections each year. Other try-panosomes cause leishmaniasis, Chagas' disease, and East Coast fever; all are major diseases in the Tropics.

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Responses

  • RUBY
    What is different about the mitochondria of diplomonads and parabasalids?
    7 years ago
  • ethan
    Which clade has an undulating membrane?
    7 years ago
  • laura pray
    What do diplomonads and parabasalids have in common?
    7 years ago
  • abbie
    What is unique about the mitochondria of diplomonads and parabasalids?
    7 years ago
  • kathryn
    Are diplomonads photosynthetic?
    7 years ago
  • ROSAMUNDA
    What is the undulating membrane in a protista?
    7 years ago
  • Jarno
    What is the protist group of diplomonads?
    7 years ago
  • Stefan
    Are parabasalids unicellular?
    7 years ago
  • torsten
    What group of organisms possesses undulating membrane?
    7 years ago
  • noora
    Why do diplomonads have two nucleus?
    7 years ago
  • Franziska
    Where to find diplomonads and parabasalids?
    7 years ago
  • markus eichmann
    What is the location of diplomonads and parabasalids?
    7 years ago
  • kifle
    Where are diplomonads and parabasalids located?
    7 years ago
  • christina baum
    Where are diplomonads and parabasalids found?
    7 years ago
  • domenica
    What protist group contains a single flagellum and an undulating membrane?
    7 years ago
  • clara
    Which of these groups is flagellated protist a parabasalids b euglenoids?
    7 years ago
  • Markus
    Which protist mutagen bleach?
    7 years ago
  • tanya
    How does diplomonads spread?
    7 years ago
  • anja
    What enviorments is protist in .?
    7 years ago
  • yvonne radcliffe
    What is the mode of movements for diplomonads?
    6 years ago
  • daniel
    Are diplomonads and paprebasalids no motile?
    6 years ago
  • Elisa
    How are euglenozoans and diplomonads related?
    6 years ago
  • medhanie
    How do diplomonas and parabasalids survive without mitochondria?
    6 years ago
  • fraser davidson
    How parabasalids and diplomonads survive without mitochondria?
    6 years ago
  • Everard
    Why do diplomonads have 2 nuclei?
    6 years ago
  • adalfredo
    Are diplomonads and parabasalids in different clades?
    5 years ago
  • leonie
    What is the domain of diplomonads?
    5 years ago
  • Stuart
    Are parabasalids multicellular?
    5 years ago
  • mewael
    How do Diplomonads infect humans?
    5 years ago
  • lavinia brown
    How many species of diplomonads are there>?
    5 years ago
  • danny
    How do parabasalids function?
    5 years ago
  • Mezan
    How many nuclei do parabasilids have?
    3 years ago
  • MYLA
    How do diplomonads work?
    3 years ago
  • carla
    How do diplomonads get nutrition?
    3 years ago
  • peter
    What enviroment do diplomads and parabasalids prefer?
    3 years ago
  • Miniya
    What unique features will be found about Nuclei in diplomonads?
    2 years ago
  • priscilla de luca
    Do diplomonads reproduce asexually?
    2 years ago
  • Hiewan
    Why do diplomonads lack mitochondria ans we rs?
    2 years ago

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