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Biology 1002B Study Guide - Midterm Guide: Horizontal Gene Transfer, Stop Codon, Ribosomal Rna

Course Code
BIOL 1002B
Tom Haffie
Study Guide

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Lecture 10 - Evolution of Eukaryotes
Meaning of endosymbiosis
A living organism living within the cell of another living organism - they help
each other out.
Origin of endomembrane system, nuclear membrane, ER, etc
The endomembrane system (nuclear envelope, ER) was thought to have been
derived from infolding of the plasma membrane (supported by the face that ER
is connected to the nuclear envelope.
Having a nuclear envelope and a nucleus allowed for compartmentalization and
was critical
**Development of the n.e and ER is NOT part of endosymbiosis.
Origin of mitochondria and chloroplasts
Mitochondria and chloroplasts are not derived from the same place the nuclear
envelope was derived
Mitochondria is said to have derived from an aerobic bacterium after a larger
primitive cell brought it in through phagocytosis - it being the mitochondria.
Chloroplast is said to have descended from a cyanobacteria
‘Aerobic bacterium’ that had mitochondria engulfed a cyanobacteria (lead to
plants and such)
Top branch gets you plants, algae, etc
Bottom branch gets you animals,
fungi, etc
So, aerobic bacterium (free living bacteria) was engulfed and then evolved into
the mitochondria over time
A subset of those primitive cells that engulfed aerobic bacterium then engulfed
Bacteria that can
undergo oxidative
May have been an
anaerobic bacterium that
had an endomembrane

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Evidence supporting theory of endosymbiosis
1) Morphology - mitochondria look like bacteria (similar shape and what not) AND
chloroplast kind of looks like cyannobacteria
2) Mitochondria/chlorplast divide within a living cell identical to the way bacteria
3) Mitochondria and chloroplasts are the only organelles within eukaryotic cells
that have electron transport chains which means they probably did electron
transport when they were free living cells as well
4) They have their own genomes (circular chromosomes)
5) They have transcription and translation machinery - have their own ribosomes
and make their own proteins.
6) Mitochondria and chloroplast structure is very similar to prokaryotic cell
Factors driving development of early eukaryotic cells
OXYGEN - about 2.2 bya cyanobacteria developed and they could do oxidative
phosphorylation (split water - release oxygen into atmosphere)
This paved the way for aerobic respiration --> provides MUCH more ATP than
glycolysis and fermentation --> cell can now make more energy.
Why eukaryotic cells can be larger and more complex than prokaryotes
Bacteria and Archaea have their centers of oxidative phosphorylation on their
plasma membranes. So, if they try to get bigger, they need more centers of
oxidative phosphorylation to give them more energy.
Problem is that prokaryotes’ plasma membrane’s surface area increases as a
function of radius SQUARED whereas the volume increases as a function of
radius CUBED
Volume gets bigger much quicker than surface area of plasma membrane and
so the cell tries to compensate by putting more centers of oxidative
phosphorylation on the plasma membrane BUT eventually it runs out of space
on the p.m and that is what limits the size of prokaryotes (not being able to
produce enough energy to support a larger cell)
Prokaryotic Cells have a HIGH plasma membrane area to volume ratio
A = 4 πr2
V = 4/3 πr3

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However, eukaryotes can be much bigger because you have mitochondria and
each mitochondria has many ox-phos centers and so you can produce MUCH
more ATP and support a larger cell/genome
LOW plasma membrane surface area to volume in eukaryotes.
Eukaryotic cell has more energy to invest into protein synthesis and as a result
can generate/express more proteins that are often more complex.
Evidence for lateral gene transfer from organelles to the nucleus
Genes that code for proteins found in mito/chloro are not found and expressed
in the nucleus ( e.g - proteins that make up complex 1)
General idea about how lateral gene transfer is detected (Southern Blot)
Isolate genomic DNA , run it on gel (make DNA single stranded)
Add a single stranded DNA probe and see if hybridization occurs
You can then see what genes you have in that genome.
So you can isolate mitochondrial DNA, and nuclear DNA and add the probe of
Oxidase 3 (mitochondrial gene)
If the gene is found mtDNA but not the nDNA - Lateral gene transfer has not
If found in nDNA and not mtDNA - lateral gene transfer has occurred
If found in both, LGT occurred and both genomes have a copy of this gene.
Hypothesis for why genes move to the nucleus from organelles (lateral gene
Coordinated control / put them under tighter nuclear control
Integrates the metabolism of the entire cell (see lecture 11)
Possible reasons why certain genes have NOT moved to the nucleus from
Lecture 11
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