Eukaryotic cells and Protists

• Eukaryotes include single-celled and multi-celled organisms.
• Eukaryotic cells have membrane-bound organelles and cytoskeletons.
• Eukaryotes intake nutrients through various forms and show a complex phylogeny.

Protists

• Protista is the informal name of the "kingdom" of mostly unicellular eukaryotes, although this kingdom is no longer valid.
• Eukaryotic systematics have caused the classification of protists to change significantly.
• Protists form a paraphyletic group.
• Protists are more complex than bacteria and archaea because they are eukaryotes with organelles.
• Not animals, plants, or fungi, protists are all eukaryotes.
• Most protists are unicellular; however, some colonial and multicellular species exist.

Basic Eukaryotic Biology

• Eukaryotes display greater structural and functional diversity than any other domain.
• Single-celled eukaryotes are complex; organelles in each cell carry out all biological functions.
• Eukaryotes exhibit nutritional diversity including:
  • Photoautotrophs contain chloroplasts.
  • Heterotrophs absorb organic molecules or ingest large particles of food.
  • Mixotrophs combine photosynthesis and heterotrophic nutrition.
• Eukaryotes can reproduce sexually or asexually.
• Mitosis in unicellular eukaryotes differs from the process in multicellular eukaryotes.
• Meiosis is specific to eukaryotes.
• Endosymbiosis is considered the origin of much Eukaryote diversity.
• Mitochondria evolved through the endosymbiosis of an aerobic bacterium.
• Plastids evolved through the endosymbiosis of a photosynthetic cyanobacterium.
• Red and green algae are the product of the plastid-bearing lineage of eukaryotes.
• Red and green algae underwent secondary endosymbiosis during eukaryotic evolution.
• During secondary endosymbiosis, red and green algae were ingested by a heterotrophic eukaryote.

Supergroups of Eukaryotes

• All eukaryotes are divided into six supergroups.
• It is no longer considered that amitochondriates (lacking mitochondria) are the oldest lineage
• Understanding relationships among eukaryotic groups continues to change.

Excavata

• One of the six supergroups of Eukarya that includes diplomonads, parabasalids, and euglenozoans.
• Excavata clade is characterized by its cytoskeleton.
• Diplomonads:
  • Have modified mitochondria called mitosomes.
  • Are often parasites, like Giardia intestinalis.
• Parabasalids:
  • Have reduced mitochondria called hydrogenosomes.
  • Include Trichomonas vaginalis, a yeast infection pathogen in human females.
• Euglenozoa:
  • Diverse clade has a crystalline or spiral rod inside their flagella, its function is unknown.
  • Some are oblige photoautotrophs, but most are heterotrophs
• Kinetoplastids
  • Have a single mitochondrion with an organized mass of DNA called a kinetoplast.
  • Many are parasitic Trypanosomes - cause African sleeping sickness, Chagas disease, and leishmaniasis.
• Euglenids
  • Have one or two flagella that emerge from a pocket at one end of the cell.

Chromalveolata

• The Chromalveolata clade is monophyletic, it originated by a secondary endosymbiosis event with red algae.
• Controversial clade includes the alveolates and the stramenopiles
• Superphylum Alveolata protists contain membrane bounded sacs (alveoli) just under the plasma membrane.
• Alveolata includes the dinoflagellates, apicomplexans, and ciliates.
• Phylum Dinoflagellates:
  • Are diverse mixotrophs and heterotrophs found in aquatic ecosystems.
  • Are components of marine and freshwater phytoplankton.
  • Shaped characteristically and internally reinforced by cellulose plates.
  • Dinoflagellate blooms cause toxic "red tides". Tides may not all be red or harmful.
• Phylum Apicomplexa:
  • Parasites in animals and cause serious human diseases.
  • The apex is specialized to penetrate a host.
  • Most have sexual and asexual stages requiring two or more different species of hosts.
  • Plasmodium, an apicomplexan, is a parasite causing malaria. - Both mosquitoes and humans are required for completion of the Plasmodium lifecycle. - Approximately 2 million people die from malaria each year. - Sickle-cell anemia is known to provide some protection.
• Phylum Stramenopila
  • Diatoms - unicellular algae with a unique two part glass-like wall of hydrated silica.
  • Golden algae - unicellular or colonial. named for their color, which results from their yellow and brown carotenoids,
  • Brown algae - includes the largest and most complex algae. - Multicellular and mainly marine. - Includes many species of seaweed. - Algal body does not have true leaves, stems, or roots and it is called a thallus. - Holdfast anchors to the stemlike stipe, supporting leaflike blades.
• Alternation of generations and the alteration of multicellular haploid and diploid forms is an aspect of complex life cycles among multicellular algae. Heteromorphic generations are structurally different versus isomorphic generations look similar.

Rhizaria

• Rhizaria is supported by DNA evidence as a monophyletic clade.
• Amoebas move and feed by pseudopodia; some, but not all, belong to the Rhizaria clade.
• Forams and radiolarians are rhizarians.
  • Both groups have hard shells known as tests, through which pseudopodia extend.

Archaeplatida

• Archaeplastida includes red algae, green algae, and land plants used as a supergroup by some scientists.
• A heterotrophic eukaryote acquired a cyanobacterial endosymbiont over a billion years prior.
• The ancient eukaryote photosynthetic descendants evolved into red and green algae.
• Descended from green algae, land plants.
• Red algae are reddish in color due to phycoerythrin which masks the green chlorophyll.
• Multicellular and contain many species of seaweed
• Green algae - includes plants
  • Named for their grass-green chloroplasts.
  • Descended from green algae, plants.
  • Chlorophytes and charopphyceans are the two main groups.
  • Most chlorophytes exist in freshwater, many are marine.
• Other chlorophytes exist as symbionts in lichens or in damp soil or snow.

Unikonts

Proposed supergroup in eukaryotes: encompasses fungi, animals, and closely related eukaryotes.

• Includes animals, fungi and closely related eukaryotes.
• Amoebozoans
  • Well supported clade.
  • Includes Ameobas and Slime molds.
• Unikonts contain two major clades - Amoebozoa and the Opisthokonta clades
  • Opisthokonts are Fungi and Animals (to be discussed later in the course).