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Lecture 4

BIOL 215 Lecture Notes - Lecture 4: Chlamydomonas, Oogamy, Rhizaria


Department
Biology (Sci)
Course Code
BIOL 215
Professor
Neil Price
Lecture
4

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BIOL215 Lecture 4 Notes
The consequences of O2 production includes:
Allowed for the evolution of a new type of metabolism - aerobic metabolism: greater energy yield
per mol of C substrate consumed
Changed ocean chemistry: S and N oxidation (SO4
2- collects in ocean)
Allowed for the formation of the ozone layer - O3 protection from UV
Poisoned environment - anaerobic organisms became confined to refuge habitats
Organisms had to evolve mechanisms to detoxify the noxious by-products of O2 - superoxide,
hydrogen peroxide...
The release of O2 by photosynthesis is perhaps the single most significant effect of life on the
geochemistry of the Earth
In Phanerozoic period, the increased fluctuation of oxygen in the environment allowed for the
evolution of larger animals
Origins of Eucaryotes:
Cells existing prior to 1.8 (2.7) bya were all prokaryotes: bacteria and archaea
Eukaryotes appear in the fossil record ca. 1.8 bya
Chemical markers (steranes) produced only by eukaryotes are detected in rocks (roughly 2.7 bya)
How did eucaryotes differ?
Prokaryotes have no nucleus, organelles, or microtubules and have 70S ribosomes. They have an
outer cell wall composed of peptidoglycan (bacteria, but not archaea). They are generally small, <2
micrometer in diameter
Eukaryotes were much larger (100-1000x larger in size), have a nucleus, have lots of organelles
and microtubules.
Endosymbiotic theory of origin of eucaryotes:
Theory proposed by Lynn Marguilis
Mitochondria and chloroplasts of eucaryotes were at one time free-living bacteria that were
engulfed by an archaea and evolved an obligatory symbiosis (a relationship between two
organisms that benefits both)
Mitochondria - proteobacterium
Chloroplast - cyanobacaterium
Theory very strongly supported by data
Theory believed that host archaeon with membranes, cytoskeleton, and a nucleus then engulfed
either a proteobacterium or cyanobacterium
Evidence for endosymbiotic theory:
Organelles (chloroplasts and mitochondria):
1. Contain own DNA, similar to bacterial DNA, no histones, circular
2. Are surrounded by a double membrane - the inner one looks like a bacterial membrane
3. Show antibiotic sensitivity (use antibiotics and show that you can inhibit their replication like
with bacteria)
4. Have ribosomes (70S) like bacteria (eukaryotes have 80S)
Secondary endosymbiosis:
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In 2 groups of protists, we can still see the evidence of a second endosymbiotic event. The
nucleomorph: a remnant of the nucleus of the endosymbiotic in the chloroplast!
Biodiversity I
Method for organizing information
Grouping similar organisms together
Historically, it involved grouping organisms into different categories based on their physical
characteristics (hard for microbes)
Ideally it should reflect the evolutionary distances and relationships among organisms
Predict characteristics of newly described organisms
Understand the history of life
Difficulty in classifying microorganisms:
Morphologically simple - they have fewer obvious features that can be used to measure
relatedness of species
RNA proposed because it is found in all organisms
Transmission of genetic information captures ancestral relationships
Slowly changing
Large enough to record useful information on evolutionary change
Two kingdoms of organisms:
Created by Aristotle
Plantae and Animalia
20th Century
Single-celled organisms (prokaryotes) and single and multicellular organisms (eukaryotes)
Problem with two kingdoms became five
Prokaryotes are NOT monophyletic (a group of organisms that contains all its descendants and
its ancestor) branches of the tree of life; they are two separate lineages that evolved similar
character states (polyphyletic)
Five kingdoms, one for prokaryotes and four (protists, fungi, plants, and animals) to cover
eukaryotes
Molecular phylogeny:
RNA sequence analysis identifies 3 major lineages (called domains) (Carl Woese 1977):
Bacteria (prokaryote)
Archaea (prokaryote)
Eucarya (eukaryote)
Classification within each domain is based on rRNA or more recently using a number of different
genes
Horizontal gene transfer and the tree of life:
What if the genes were not only transferred vertically from parent to offspring (ancestor to
descendent)?
During endosymbiosis genes transferred from the endosymbiont to the host genome (EGT) plus
EGR (Endosymbiotic gene replacement)
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