Biology 2581B Lecture Notes - Lecture 2: Alphaproteobacteria, Lokiarchaeota, Nucleomorph
19 Feb 2018
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Lecture 2
Genome → a set of genetic instructions within a compartment
Oxytricha
-type of ciliate ∴ eukaryote
-2 nuclei and 2 diff nuclear genomes
•two nuclei not because one is a nucleomorph
-where telomerase was initially observed
•think: HAHA tricked you, i have two nuclei and telomerase
Lecture 3:
1) Endosymbiosis that gave rise to eukaryotic cells/complex cells &
organisms/complex genomes & genetic compartments 1.8 bya
Lokiarchaeota (Loki) → archaeal host; replication system (i.e.information
transmission) of archaea is homologous to that of eukaryotes
Alpha-proteobacterium → bacterial endosymbiont; bacterial membranes,
metabolic enzymes, signal transduction pathways are homologous to
eukaryotic membranes (note: bacterial genes outnumber the archaeal
genes about two-fold)
2) Endosymbiosis that gave rise to plants and algae (i.e. genetic merger of 3 distinct lineages)
(1.5bya)
Cyanobacterium → could photosynthesize; was engulfed by Loki (archaea) that already had
engulfed an alpha-proteobacterium
∴ the genetic merger that gave rise to photosynthetic cells happened after the endosymbiotic
event that gave rise to eukaryotes
→ more than 50% of our genes come from an endosymbiont (i.e. the endosymbiotic footprint of
the bacterial endosymbiont is >50%!!)
3) Endosymbiosis between photosynthetic eukaryote and a non-photosynthetic eukaryote
-i.e. the NP eukaryote prays on the P eukaryote
-resulted in a 2º chloroplast
-called 2º because it’s not from cyanobacteria, rather another eukaryote
Sequence of events in a genetic merger
1) Feeding (organism A feeds on B)
2) Endosymbiosis (organisms B undigested & inside A)
3) Sharing (host and endosymbiont share resources; host-endosymbiont relationship)
4) Entrapment (gene loss → ratchet)
5) Transfer of control (endosymbiontic gene transfer → when genes from the endosymbioatn
transfer to the host’s genome)
6) Genetic integration (almost all of the endosymbiont genes lost of transferred to host → A
and B become a single organism)
mnemonic → feel entire schlongs entirely tremendous girth
- steps 4) 5) and 6) and evolutionary ratchets → i.e. endosymbiotic gene loss and
endosymbiotic gene transfer are evolutionary ratchets
find more resources at oneclass.com
find more resources at oneclass.com
Positioning the eukaryote branch – Tree of Life
-bias is given to the host cell ∴ eukaryote branch off of archaea
-but it’s more correct to show that eukaryotes branch from both archaea and bacteria
-some ppl argue that it’s most correct that eukaryote domain should be embedded within
archaeal domain
Lynn Margulis → 1st proposed that endosymbiosis and genetic mergers gave rise to complex
cells
Endosymbiosis and Genetic Mergers Summary:
-endosymbiosis gave rise to complex cells
-blending of genomes and DNA provide the genetic template for complexity
-endosymbiosis and genetic mergers provided the genetic template for diversity
Lecture 4: Organelles and their genomes
→ eukaryotes and archaea are equally distantly related to bacteria
Carl Woese → proposed that archaea represent a third domain of life based on archaea’s rRNA
-due to discovery of Loki (a very close archaeal relative to eukaryotes, it suggest that
eukaryotes grew out of archaea rather than in parallel; i.e. we are a daughter to archaea, not
a sibling
-from this, the 3 domain tree of life is now two branches (archaea and bacteria)
Spread of photosynthesis:
-recall: 1.5bya a cyanobacteria entered a eukaryote cells → chloroplasts
-this happened ONCE in evolution
-then a non-photosynthetic eukaryote engulfed a photosynthetic eukaryote → 2º chloroplasts
-this happened on at least 3 separate occasions
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Genome a set of genetic instructions within a compartment. 2 nuclei and 2 diff nuclear genomes: two nuclei not because one is a nucleomorph. Where telomerase was initially observed: think: haha tricked you, i have two nuclei and telomerase. Lecture 3: endosymbiosis that gave rise to eukaryotic cells/complex cells & organisms/complex genomes & genetic compartments 1. 8 bya. Lokiarchaeota (loki) archaeal host; replication system (i. e. information transmission) of archaea is homologous to that of eukaryotes. Cyanobacterium could photosynthesize; was engulfed by loki (archaea) that already had engulfed an alpha-proteobacterium. The genetic merger that gave rise to photosynthetic cells happened after the endosymbiotic event that gave rise to eukaryotes. More than 50% of our genes come from an endosymbiont (i. e. the endosymbiotic footprint of the bacterial endosymbiont is >50%!!: endosymbiosis between photosynthetic eukaryote and a non-photosynthetic eukaryote. I. e. the np eukaryote prays on the p eukaryote. Called 2 because it"s not from cyanobacteria, rather another eukaryote.
