LO4

eukaryotic innovations

• membrane-bound organelles (including nucleus)

• complex cytoskeleton

  • their flagella (and cilia) have a 9+2 arrangement of microtubules

• multiple, linear chromosomes in their nucleus

• can be multicellular (but many protists and some fungi are unicellular)

• undergo cell division using mitosis and meiosis and cytokinesis

• many have sexual reproduction (some also have asexual, or only asexual)

how did eukaryotes evolve?

• evolved from simpler prokaryotic cells > 2.2 bya

• the earliest eukaryotes were unicellular

• Plasma membrane infolding may explain the origins of many

  eukaryotic organelles, including the nucleus and ER

plasma membrane infolding

• explains the origins of many eukaryotic organelles, including the nucleus and ER

• infolding is a common phenomenon; modern cyanobacteria have an infolded plasma membrane for photosynthesis enzymes

serial endosymbiosis

explains the origins of mitochondria and chloroplasts. It states that the ancestors of mitochondria and chloroplasts were free-living bacterial cells prior to 2.2 bya

origins of the mitochondrion

• prior to 2.2 bya, some free-living aerobic bacteria were engulfed by larger host cells

• they became aerobic endosymbionts inside of their likely anaerobic hosts

• eventually, the endosymbionts could not survive outside of the host= permanent mutalism

  • the endosymbionts eventually became mitochondria

origins of the chloroplasts

• ancient cyanobacteria were engulfed by larger, heterotrophic eukaryotic host cells that already had mitochondria

• these cyanobacteria became photosynthetic endosymbionts in their host

• eventually these endosymbionts could not survive outside of their host and became chloroplasts

• chloroplast evolution likely involved multiple endosymbiotic events

primary endosymbiosis

gave rise to chloroplasts in the archaeplastids (red algae, green algae, and land plants)

secondary endosymbiotic events

other photosynthetic eukaryotes (e.g. dinoflagellates, brown algae) evolved

evidence for serial endosymbiosis

• mitochondria and chloroplasts have their own genetic material and protein synthesis machinery

• both have a single, circular DNA genome (DNA sequences are similar to certain aerobic bacteria and cyanobacteria)

• replicate by binary fission

• have a double membrane (outer membrane was derived from the host cell during the engulfing process)

eukaryotic phylogeny

• determined primarily based on DNA and cell structure

  • former kingdom protista is paraphyletic

  • 5 clades

  • some homoplasius traits such as multicellularity and photosynthesis

5 clades

• three clades contain only protists

  • excavates, chromalveolates, and rhizarians

• two clades contain protists and other eukaryotic groups

  • the archaeplastid clade also includes the land plants, and the unikont clade also includes the fungi and animals

diversity of protists

• mostly unicellular eukaryotes typically found in aquatic habitats

  • the base of aquatic food chains

  • motile

  • reproduce asexually

protists as the base of aquatic food chains

• photoautotrophic protists (i.e. algae) are important primary produces (produce organic molecules during photosynthesis)

• chemoheterotrophic protists are typically free-living and ingest food, often by phagocytosis, but some are pathogens

motile protists

• some move via pseudopodia: cytoplasm extensions that allow for a crawl-like movement

• other move via flagella (a long, whiplike movement organelle) or cilia (short, hair-like movement organelles)

dinoflagellates

• flagellate chromalveolates

• phytoplankton

• cause red tide

• zooxanthellae in corals

phytoplankton

floating aquatic organisms that are photosynthetic. primary producers and food source

red tide

an algae population bloom in warm nutrient rich coastal waters. Algae produce toxins that can kill marine organisms and contaminate human food sources (e.g. shellfish)

zooxanthellae

dinoflagellates that are endosymbionts of corals. The provide nutrition to their coral hosts through photosynthesis

corals hosts provide shelter and inorganic nutrients (N, P, CO₂)

apicomplexans

• animal parisites

• use an apical complex of microtubules to attach to their animal host. They usually require more than one host to complete their life cycle

plasmodium

an apicomplexan that causes malaria. It undergoes sexual reproduction in mosquito hosts, and asexual reproduction in human hosts. it infects human blood and liver tissues. Destruction of red blood cells causes the characteristic symptoms of malaria (i.e. fever, chills)

brown algae

• a type of chromalveolate

• multicellular algae (seaweeds) in shallow marine habitats

• provide primary productivity, food and structure to cold-water kelp forest ecosystems. Giant kelp can grow up to 200 ft

seaweeds

have a plant-like body, with structures for capturing sunlight for photosynthesis and anchoring to the ocean floor. Use gas bladders (gas filled spheres) for flotation

archaeplastids

• arose from primary endosymbiosis

• red algae, green algae, and plants

• all photoautotrophs and share a similar chloroplast structure

• green algae are the closest relatives of land plants

unikonts

• a clade of heterotrophic eukaryotes that have a single posterior flagellum in flagellated cells (e.g. sperm, spores).

  • all other eukaryotes are bikonts that have two anterior flagella in any cells that are flagellates

opisthokonts

• subclade of unikonts that includes the fungi, choanoflagellates, and animals

choanoflagellates

aquatic, unicallular protists. Evolutionary important because they are the closest relatives of animals. the structure of choanoflagellate cells is very similar to that of the feeding cells of sponges. (simple animals)