1. Lecture 21. Basic Architecture of the Eukaryotic Cell, Symbioses, Early Eukaryote Fossils. reading: Chapter 5

2. Basic Structure of the Prokaryotic Cell Prokaryotes = Archaea + Bacteria Prokaryotes- lack nucleus/nuclei

3. Basic Structure of the Eukaryotic Cell Eukaryote (“true nucleus”) are much more complex DNA containing organelles (“little organs”) nucleus mitochondrion - respiration chloroplast - photosynthesis } were once free-living prokaryotes often have multiple chromosomes (linear chromosomes) lots more genes lots of “junk DNA” in their genes

4. Eukaryotes are Typically Larger than Prokaryotes

5. Organelles (“ little organs ”) Found only in eukaryotes. Were once free-living Bacteria. How do we know this? -have their own genomes -genomes are circular -have 16S rRNA genes chloroplast branches in Cyanobacteria - oxygenic photosynthesis mitochondria branches in Proteobacteria near Rickettsia- aerobic respiration -have lipid membranes (often two sets) -one species of alga still has peptidoglycan cell wall around its chloroplast

6. Endosymbiosis Host cell engulfed a prokaryote cell: -many protozoa ingest prokaryote cells as a food source ( endocytosis and then digest cells) -maybe they didn’t digest the cells one day -stably maintained endosymbiont symbiosis - a mutually beneficial relationship

7. Endosymbiosis, cont. mitochondria and chloroplasts contain two or more sets of membranes

8. Serial Endosymbiosis

9. Algae with Primary Endosymbionts Green Algae (& Plants) Red Algae Cyanophora

10. Algae with Secondary Endosymbionts Diatoms Dinoflagellates Golden Brown Algae Brown Algae/ Kelps Yellow Algae Cryptomonads Chlorarachniophytes

11. Organelles Mitochondria: - nearly all eukaryotes have them - some have modified them so they no longer do aerobic respiration - some have lost them - eukaryote ancestor likely had mitochondria - engulfment likely happened once Chloroplasts: - most eukaryotes don’t have them - independent lineages have them - acquired late - original primary engulfment likely happened once - secondary engulfments occurred - some have lost their chloroplasts chloroplast of a golden brown algae showing >2 membranes

12. Ancient Lipids 2.7 Ga Eukaryote lipids ( steranes ) and Cyanobacterial lipids. Need oxygen to make steranes. What does this suggest about the presence of O 2 2.7 Ga?

13. Early Fossil Record of Eukaryotes Acritarchs: spherical microfossils thought to be unicellular algae large diameters (20 - 150 µm) thick organic cell walls - easily preserved first appear ~1.7 Ga

14. Later Acritarchs More Diverse Cambrian 560 Ma spiny acritarch Upper Ordovician Cyst broken - dormant cell released all images: copyright Cushman Foundation for Foraminiferal Research

15. Grypania spiralis 1.3 Ga ~0.5m in length. Found in shales and slates from Montana, China, and India. Not known what organism this once was. Animal? Plant? Algae? Extinct kingdom?

16. Fossil Red Algae (?) 1.2 Ga Distinctive cell division patterns found only in the red algae. First occurrence of complex multicellularity in the fossil record. Also first evidence of sexual reproduction.

17. reading: Chapter 5 Lecture 22. Evolution of Multicellularity, Colonization of Land.