BCOR 1450 Module 3: Protists

Define protists

• Any eukaryotic organism that is not a plant or animal

• Make up majority of eukaryotic lineages

• Unicellular w/ elaborate subcellular organelles including some absent in other organisms

Describe endosymbiotic theory

Endosymbiotic theory: includes 2 primary endosymbiotic events that contributed to the rise of eukaryotes

• Plasma membrane of ancestral prokaryote folds in, which develops into the first endomembrane system

• FIRST PRIMARY EVENT: a cell with an endomembrane system engulfs aerobic bacterium which becomes the mitochondria

• SECOND PRIMARY EVENT: an ancestral eukaryotic cell with an endomembrane system and mitochondria engulfs a photosynthetic bacterium (cyanobacteria) which develops into a plastid

  • Plastid: membrane bound organelle found mostly in algae, plants and other eukaryotes, diversified into chloroplasts.

Provide evidence to support endosymbiotic theory

• Cells cannot make mitochondria

• Mitochondria and chloroplast have own circular DNA, ribosomes, and double membranes, resembling bacteria

• When mitochondria releases mtDNA, immune sys. attacks as it would bacteria

What is the significance of endosymbiosis?

• Mitochondria allows Cells to produce significantly more ATP through cellular respiration than previously being produced via glycolysis

• Excess ATP supports complex function: specialized cells and multicellularity arise

• Stramenopiles and alveolates able to photosynthesize due to plastids

What is the difference between primary and secondary endosymbiosis?

• Primary endosymbiosis is an initial event where a heterotrophic eukaryotic cell engulfs a prokaryote that eventually becomes an organelle (as described above)

• Secondary endosymbiosis occurs when a eukaryotic cell engulfs another eukaryotic cell that already has already undergone primary endosymbiosis and possesses a plastid

Euglenozoans

Taxonomy: Excavata

Key morphology: Single celled, flagellated

Habitat: Diverse

Feeding: Diverse

Diatoms

Taxonomy: SAR, Stramenopiles

Key morphology: Unicellular, strong glass-like wall of silicon dioxide allowing for fossilization

Habitat: Aquatic

Feeding: Photosynthetic

Dinoflagellates

Taxonomy: SAR, Alveolates

Key morphology: Unicellular, whip like flagella causing locomotion

Habitat: Mostly aquatic

Feeding: Diverse

Cercozoans

Taxonomy: SAR, Rhizaria

Key morphology: Amoeboid and flagellated with pseudopodia

Habitat: Aquatic and soil

Feeding: Mostly heterotrophic