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Lecture 4

BIOL 215 Lecture Notes - Lecture 4: Charophyta, Sexual Reproduction, Chemotroph

Course Code
BIOL 215
Neil Price

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Consequences of Oxygen Production
-Allowed for a new type of metabolism which had a greater energy yield compared to
the previous one (aerobic vs anaerobic)
-Greater energy yield per mol of C substrate consumed
-Ocean chemistry changed: S and N oxidation (sulphates collect in ocean)
-Ozone layer forms acting as a protective layer from UV light
-Oxygen presence caused aerobic organisms to seek other habitats because it is
poisonous to them.
-Organisms also had to evolve to detoxify noxious by products of oxygen such as
superoxide, hydroxide peroxide
Origin of Eukaryotes
-Eukaryotes appear in fossil record at around 1.8 bya
-Chemical markers such as steranes produced only by them are detected in rocks
around 2.7 bya
-Differ from prokaryotes
Eukaryotes: have a nucleus, 80S ribosomes, mitosis, organelles
Prokaryotes: have no nucleus, organelles, or microtubules and have 70S ribosomes,
binary fission
Endosymbiotic Theory
-Mitochondria and chloroplasts used to be free living organisms (bacteria) that were
engulfed by an Archaea and evolved to take part in a symbiotic relationship.
-Mitochondria: proteobacterium
-Chloroplast: cyanobacterium
Evidence for this Theory
-Organelles such as chloroplasts and mitochondria
1. Contain own DNA similar to bacterial DNA (no histones, circular)
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2. are surrounded by a double membrane (inner one looks like a bacterial
3. Show antibiotic sensitivity
4. have ribosomes 70S like bacteria (whereas the cytoplasm of cell has 80S)
Secondary Endosymbiosis
-In 2 groups of protists, evidence is still visible of a second endosymbiotic event called
The Nucleomorph: a remnant of the nucleus from the 1st endosymbiosis
-Cryptomonad cell formed from this secondary event
-Method of organizing the groups of organisms
-Should reflect the evolutionary distances and relationships among organisms
-Difficulty in classifying microorganisms—they have fewer obvious features that can
be used to measure relatedness of species.
Molecular Phylogeny
-RNA gene sequence analysis identifies 3 major lineages
1. Bacteria (prokaryote)
2. Archaea (prokaryote)
3. Eukarya (eukaryote)
- Eukarya share a common ancestor with Archaea
Horizontal Gene Transfer (HGT) & Tree of Life
-Gene transferred from unrelated bacterial species through plasmids or other
-During endosymbiosis genes were transferred from the endosymbiont to the host
genome (EGT)
-HGT is also affected by a virus or small circular DNA known as a plasmid
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