Download Lecture21

Lecture 21. Basic Architecture of the Eukaryotic
Cell, Symbioses, Early Eukaryote Fossils.
reading: Chapter 5
Basic Structure of the Prokaryotic Cell
Prokaryotes = Archaea + Bacteria
Prokaryotes- lack nucleus/nuclei
Basic Structure of the Eukaryotic Cell
often have multiple chromosomes
Eukaryote (“true nucleus”)
(linear chromosomes)
are much more complex
lots more genes
DNA containing organelles (“little organs”)
lots of “junk DNA” in their genes
nucleus
mitochondrion - respiration
were once free-living prokaryotes
chloroplast - photosynthesis
}
Eukaryotes are Typically Larger than Prokaryotes
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
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
Endosymbiosis, cont.
mitochondria and chloroplasts contain two or more sets of membranes
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Serial Endosymbiosis
Algae with Primary Endosymbionts
Cyanophora
Green Algae
(& Plants)
Red Algae
Algae with Secondary Endosymbionts
Golden Brown Algae
Dinoflagellates
Yellow Algae
Chlorarachniophytes
Brown Algae/
Kelps
Cryptomonads
Diatoms
Mitochondria:
Organelles
- 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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
chloroplast of a golden brown
algae showing >2 membranes
Ancient Lipids
2.7 Ga
Eukaryote lipids (steranes) and Cyanobacterial lipids.
Need oxygen to make steranes.
What does this suggest
about the presence of O2
2.7 Ga?
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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Later Acritarchs More Diverse
Cambrian 560 Ma
spiny acritarch
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Upper Ordovician
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Cyst broken - dormant cell released
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
all images: copyright Cushman Foundation for Foraminiferal Research
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?
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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.
Lecture 22. Evolution of Multicellularity,
Colonization of Land.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
reading: Chapter 5