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Lecture 10

Biology 1002B Lecture Notes - Lecture 10: Southern Blot, Cytoskeleton, Trichomonas

Course Code
BIOL 1002B
Denis Maxwell

of 2
Lecture 10: Evolution of Eukaryotes
1. Meaning of endosymbiosis and lateral gene transfer
o Mitochondria, chloroplasts may originate from symbiotic relationships between two prokaryotes
Lateral gene transfer
o Genes from mitochondrion or chloroplast relocated to the nucleus over millions of years
o Nucleus can take control
o Only thing that changed is the relocation of the gene but not what the gene does
2. Origin of endomembrane system, nuclear membrane, ER etc.
Endomembrane series of intracellular membrane compartments found in eukaryotic cells
Membranes are similar in fatty acid and structures
Endomembrane defining characteristic of eukaryotes
o nuclear envelope derived from infolding of plasma membrane
o ER connected to nuclear envelope
o ER and nuclear envelope is very distinct from endomembrane system and endosymbiosis
(Endomembrane system) Ancestral bacterium infolding of plasma membrane nuclear envelope
and ER (endosymbiosis) aerobic bacterium cyanobacterium
Having a nucleus means you can control transcription and translation (advantageous)
o Bacteria cannot do this because everything is in the same compartment
Early cell may be anaerobic
o Small aerobic bacteria advantage with more ATP
3. Origin of mitochondria and chloroplasts
Mitochondria and chloroplast derived from free living prokaryotic cells (endosymbiosis)
o Not derived from the same place as the nucleus
Mitochondria derived from aerobic bacterium
Aerobic ancestral bacteria advantage through phagocytosis to bring aerobic bacteria to provide ATP
Chloroplast derived from cyanbacterium 2 mya
o Identical photosynthetic structure
Most eukaryotes have mitochondria
o Endosymbiosis of aerobic bacterium predated uptake of cyanobacteria
Split into animals and plants (cyanobacterium branch)
Aerobic bacterium got taken up first
4. Evidence supporting theory of endosymbiosis
Endosymbiosis between cyanobacterium, aerobic bacterium and host
o Only group of bacteria that go through oxygenic photosynthesis
o Cyanobacterium became modern chloroplasts
Identical morphology between mitochondria and bacteria
Formation and division no genes that code for chloroplast, mitochondria
Electron transport chains
o Descended from free living bacteria that can make ATP and support themselves
o Have their own genome, transcription/translation machinery
5. Factors driving development of early eukaryotic cells
o Earliest bacteria was anaerobic that got ATP through glycolysis and fermentation
o 2.2 bya, cyanobacteria
Oxygenic photosynthesis that split water, gets electrons and a higher yield of ATP
o Bacteria that undergo aerobic respiration developed
6. Why eukaryotic cells can be larger and more complex than prokaryotic cells
Oxygenic phosphorylation
o size = ↑surface area to go through ↑ ox phos on membrane = ↑↑ volume
o Volume increases much faster than surface area
o Surface area of the plasma membrane is controlling the size of prokaryotic cells
Eukaryotes have mitochondria = ↑ATP = ↑genome size and size it can support
o Mitochondria membrane is larger than plasma surface area
o Maintaining a large genome (replication) only requires 2% of ATP
o Synthesizing proteins (endergonic) takes up 75% of cellular resources
Eukaryotes have a bigger genome
o Recall that C value paradox states that genome size and size of the organisms do not correlate
o Variability in size of genome since size is not a restricting factor
o Small genome range in bacteria since smaller size is advantageous
Evolution of complex traits
o All morphologically complex life is eukaryotic
o All eukaryotes share common complex traits and none in prokaryotes
E.g. nucleus, mitosis, sex, phagocytosis, organelles, cytoskeleton, trafficking... etc.
Prokaryotes don’t show any because evolution is not gradual but stepwise
7. Evidence for lateral gene transfer from organelles to the nucleus
2 bya beginning of eukaryotic cell
Resolve the problem of who’s the boss (mitochondria, chloroplast or nucleus)
o Single cell need to coordinate
o Nucleus wants to have cellular control
Lateral gene transfer still happening today
See lecture 11 notes
8. General idea about how lateral gene transfer is detected (Southern blot)
Isolate single stranded DNA and hybridize probe
Detecting oxidase 3 gene DNA on blot
o If present in mitochondria only, it has not moved
o If present in nucleus only, it has moved
o If present in both, it is transferring to the nucleus
Caught it before it gets degraded in the mitochondria once the copy is inserted
9. Role of cpn60 in tracing endosymbiotic and lateral gene transfer event in eukaryotes.
Giardia, trichomonas
o Eukaryotic with no mitochondira
o Grows anaerobically and symbiotically (don’t need ATP)
Evidence that proves that they had and lost mitochondria
o cpn60 is a chaperone that is essential and helps mitochondria to work
o cpn60 relocates to nucleus
giardia has cpn60
o No other way to get this gene but from lateral gene transfer
Suggests that it is descended from bacteria with mitochondria
Proves that giardia are not intermediates between prokaryotic and eukaryotic cells
o cpn60 serves no function since there isn’t a mitochondria