GB 2- 03 Eukaryotes

Eukaryotic Cell Structure 

• ~ 10-100 micrometers 

• Key derived traits: 

• Nucleus 

• Membrane bound organelles (compartmentilization) 

• Well developed cytoskeleton (network of fibers within cell) 

• Cytoskeleton supports, allows for asymmetry, changing shape 

Endosymbiosis

• Relationship between 2 species, 1 lives inside the other 

• Common in evolutionary history → mitochondria and chloroplasts

Serial endosymbiosis

• series of endosymbiotic events 

Basic Process

• Heterotrophic eukaryote (w/mitochondria) engulfs cyanobacteria (1 endosymbiosis → autotrophic eukaryote w/ chloroplasts (green algae) 

• Heterotrophic eukaryote engulfs green algae (2 endosymbiosis) → autotrophic eukaryote with 2 degree plastids 

Primary Endosymbiosis

an early eukaryotic cell that already had mitochondria
engulfed a cyanobacterium (a photosynthetic prokaryote)

which then evolved into a chloroplast.

• Mitochondria (first): alpha proteobacteria (aerobic) within archaea (anaerobic) 

Second Endosymbiosis

then another eukaryote:

• engulfed a photosynthetic eukaryote (like green or red algae)
  👉 a eukaryote got eaten

result:
👉 organisms with secondary plastids

• Blogger (heterotrophic) eukaryote engulfs smaller (autotrophic) eukaryote) → secondary plastids 

Plastid

• general term for chloroplasts and related organelles 

• Chloroplasts derived from cyanobacteria (prokaryote) via primary endosymbiosis 

• Secondary plastids derived from red or green algae (eukaryotes) via secondary endosymbiosis 

Eukaryote Diversity

• Mostly Unicellular, many colonial or multicellular 

• Complex cellular organization 

• Many nutrition; strategies 

• Photoautotrophs, heterotrophs, mixotrophs

Mixotrophs

• capable to photosynthesis and heterotrophy 

Eukaryote Evolution

• prokaryotic ancestor → nucleus/endomembranes

• mitochondria via endosymbiosis

• early unicellular eukaryote diversification

• chloroplast endosymbiosis (some lineages)

• multicellularity evolves

• modern eukaryotic groups diversify

Ancestral eukaryotic traits

• Nucleus, membrane bound organelles

• Aerobic respiration

• Mitochondria from primary endosymbiosis 

Archaeplastida 

• Shared derived trait: chloroplasts via primary endosymbiosis 

• Red algae, green algae, land plants → all photosynthetic

SAR

• Shared derived trait: secondary endosymbiosis of red algae 

• Grouped based on genetic evidence 

• Includes 3 major clades

Stramenophiles: 

• SAR clade

• Shared derived traits: often have flagellum with hair like projections; often paired with smooth flagellum 

Alveolates

• SAR clade

• Shared derived trait: alveoli → flattened vesicles just inside plasma membrane → support membrane 

Rhizaria

• SAR clade

• Shared derived trait: genetic similarities: often have protective shells of calcium or silica 

Amoebozoa 

• Typical “blob” shape 

• Lobe or tube shaped pseudopodia (“false foot”)

• Ex: slime molds (not fungi) 

• Entamoebas – free-living or parasitic (entamoeba histolytica)

Opisthokonta

• Diverse group – includes animals, fungi, several groups of protists 

• Nucleariids → sister group to fungi, protists 

• Chanoflagellates → sister group to animals, unicellular 

Discoba

• Extremely diverse 

• Shared derived trait: crystalline rod in flagella 

• Some have secondary plastids via green algae → mixotrophic 

• Ex: Trypanosomes → often pathogenic 

• Euglenids → often mixotrophs