Eukaryotes Biology Notes PDF

Sushi, Ice Cream and Biofuels, Oh My Eukaryotes (just not plants, animals or fungi)  Eukaryotes The Domain, Eukaryotes, has: – Single and Multi-celled organisms – Cells with membrane bound organelles – Cytoskeletons – Various forms of energy and nutrient intake – Complex...

Sushi, Ice Cream and Biofuels, Oh My Eukaryotes (just not plants, animals or fungi)  Eukaryotes The Domain, Eukaryotes, has: – Single and Multi-celled organisms – Cells with membrane bound organelles – Cytoskeletons – Various forms of energy and nutrient intake – Complex phylogeny  Protists Protista is the informal name of the “kingdom” of mostly unicellular eukaryotes – Advances in eukaryotic systematics have caused the classification of protists to change significantly – Protists constitute a paraphyletic group, and Protista is no longer valid as a kingdom Protists are eukaryotes and thus have organelles and are more complex than bacteria and archaea Protists are all eukaryotes that are not animals, plants or fungi Most protists are unicellular, but there are some colonial and multicellular species  Multiple versions of eukaryotic tree Plenty of disputes remain and this is complicated – we will defer to the textbook Protista  Basic Eukaryotic Biology Eukaryotes exhibit more structural and functional diversity than any other domain Single-celled eukaryotes can be very complex, as all biological functions are carried out by organelles in each individual cell Eukaryotes are nutritionally diverse: – Photoautotrophs, which contain chloroplasts – Heterotrophs, which absorb organic molecules or ingest larger food particles – Mixotrophs, which combine photosynthesis and heterotrophic nutrition  Eukaryotes can reproduce asexually or sexually – Various processes occur in each – Mitosis in single celled eukaryotes differs from the process in multicellular eukaryotes Meiosis is unique to eukaryotes Mutualisms in Eukaryotes There is now considerable evidence that much Eukaryote diversity has its origins in endosymbiosis Mitochondria evolved by endosymbiosis of an aerobic bacterium Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium Brown algae underwent another round of endosymbiosis The plastid-bearing lineage of eukaryotes evolved into red algae and green algae On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote Five Six Supergroups of Eukaryotes It is no longer thought that amitochondriates (lacking mitochondria) are the oldest lineage of eukaryotes Our understanding of the relationships among eukaryotic groups continues to change rapidly One hypothesis divides all eukaryotes into six supergroups The Six Supergroups of Eukarya  Excavata The clade Excavata is characterized by its cytoskeleton This controversial group includes the diplomonads, parabasalids, and euglenozoans  Diplomonads – Have modified mitochondria called mitosomes – Are often parasites, for example, Giardia intestinalis Parabasalids – Have reduced mitochondria called hydrogenosomes – Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females  Euglenozoa Diverse clade that all have a spiral or crystalline rod of unknown function inside their flagella – Some are obligate photoautotrophs but majority are heterotrophs Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast – Many are parasitic: Trypanosomes (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 Clade is monophyletic and originated by a secondary endosymbiosis event (w/ red alga) This clade is controversial and includes the alveolates and the stramenopiles  Superphylum Alveolata protists have membrane- bounded sacs (alveoli) just under the plasma membrane Alveolata includes the dinoflagellates, apicomplexans, and ciliates  Phylum Dinoflagellates are a diverse group of aquatic mixotrophs and heterotrophs They are abundant components of both marine and freshwater phytoplankton Each has a characteristic shape that in many species is reinforced by internal plates of cellulose Dinoflagellate blooms are the cause of toxic “red tides” – Not all red tides are red – Not all red tides are harmful  Phylum Apicomplexa are parasites of animals, and some cause serious human diseases One end, the apex, contains a complex of organelles specialized for penetrating a host Most have sexual and asexual stages that require two or more different host species for completion The apicomplexan Plasmodium is the parasite that causes malaria – Plasmodium requires both mosquitoes and humans to complete its life cycle – Approximately 2 million people die each year from malaria – Sickle-cell anemia confers some protection Plasmodium life-cycle  Phylum Stramenopila (or Heterokonts) Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated silica Golden algae are unicellular (some colonial) named for their color, which results from their yellow and brown carotenoids Brown algae are the largest and most complex algae – All are multicellular, and most are marine – Brown algae include many species commonly called “seaweeds”  Brown algae The algal body is plantlike but lacks true roots, stems, and leaves Blade and is called a thallus The rootlike holdfast anchors the stemlike Stipe stipe, which in turn supports the leaflike blades Holdfast  Alternation of Generations A variety of life cycles have evolved among the multicellular algae The most complex life cycles include an alternation of generations, the alternation of multicellular haploid and diploid forms Heteromorphic generations are structurally different, while isomorphic generations look similar Alternation of Generations  Rhizaria DNA evidence supports Rhizaria as a monophyletic clade Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria Rhizarians include forams and radiolarians – Both groups have hard shells called tests – Pseudopodia extend through holes in the test  Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants Over a billion years ago, a heterotrophic eukaryote acquired a cyanobacterial endosymbiont The photosynthetic descendants of this ancient eukaryote evolved into red algae and green algae Land plants are descended from the green algae  Red Algae Red algae are reddish in color due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll Red algae are usually multicellular; the largest are seaweeds  Green Algae Named for their grass-green chloroplasts Plants are descended from the green algae The two main groups are chlorophytes and charophyceans Most chlorophytes live in fresh water, although many are marine Other chlorophytes live in damp soil, as symbionts in lichens, or in snow Green Algae Life cycle  Unikonts Proposed supergroup of eukaryotes – Includes animals, fungi and closely related eukaryotes Amoebozoans – Well supported clade – Ameobas – Slime molds Unikonts contain the groups, Amoebozoa and Opisthokonta – Opisthokonts are Fungi and Animals (to be discussed later in the course) Accept your inner nerdness  4 cm Plasmodial Slime Molds FERTILIZATION Zygote Feeding (2n) plasmodium Mature plasmodium (preparing to fruit) Flagellated Young Amoeboid cells sporangium cells (n) (n) Mature Germinating sporangium spore Spores (n) MEIOSIS 1 mm Stalk Key Haploid (n) Diploid (2n)  Spores FERTILIZATION (n) Emerging amoeba (n) Zygote SEXUAL (2n) REPRODUCTION Solitary amoebas 600 µm (feeding stage) MEIOSIS (n) Fruiting ASEXUAL bodies REPRODUCTION Amoebas (n) (n) Aggregated amoebas Migrating aggregate Cellular Key Slime Molds 200 µm Haploid (n) Diploid (2n)