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Lecture 1

BIOB10Y3 Lecture Notes - Lecture 1: Gemmata Obscuriglobus, Prokaryote, Paramecium


Department
Biological Sciences
Course Code
BIOB10Y3
Professor
Aarti Ashok
Lecture
1

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The origin of Eukaryotic cells
Prokaryotic cells arose before eukaryotic cells - fossil record
- Fossil record shows that prokaryotic cells were present in rocks approx. 2.7B years old
o Which was approx. 1B years before evidence of eukaryotes
Eukaryotic cells arise from prokaryotes
- Similarities noted between them (genetic code, metabolism)
- The two types of cells related to one another b/c they share many complex traits (e.g., very similar genetic codes,
enzymes, metabolic pathways, and plasma membranes) that could not have evolved independently in different
organisms
It was believed that the process gradual evolution causing eukaryotes to evolve from prokaryotes in which the organelles
of the eukaoti ell eae oe ople… - Wrong
Margulis hypothesis certain organelles of eukaryotic cell (most notably the mitochondria and chloroplasts) had evolved
from smaller prokaryotic cells that had taken up residence in the cytoplasm of a larger host cell referred to as
endosymbiont theory descries ho a sigle oposite ell of geate opleit ould eole fo to o oe
separate, simpler cells living in a symbiotic relationship with one another
Edosybiot theory
An endosymbiont is a combination of 2 cells living together in a symbioti elatioship; oe ell lies iside the
other cell.
edo eaig iside o ithi
o They are not just living in proximity (near) to each other but one actually lives inside of the other cell
This type of relationship is what we think led to the primitive (ancient/earliest) eukaryotic cells that
tend to be our ancestor
That’s hee all of ou iteal opleit, i tes of the iteal opoets suh as
mitochondria have got to come to arrive
- Our earliest prokaryotic ancestors were presumed to have been anaerobic heterotrophic cells:
o Anaerobic meaning, they derive energy from food matter without using molecular oxygen (O2)
o Heterotrophic meaning, they were unable to synthesize organic compounds from inorganic
precursors/ancestor (such as CO2 and water)
Instead had to obtain preformed organic compounds from their environment
- These prokaryotic ancestors are thought to have acquired the ability to form internal membrane compartments,
allowing formation of a nucleus by containing the DNA within an internal membrane
- This development of internal membranes produces the first organism that would be considered eukaryote- like in
terms of having a nucleus or other internal compartments
- B/c this is the first organism that gave rise to all eukaryotes First eukaryotic common ancestor (FECA)
- Once thought presence of internal membrane only eukaryotic trait BUT NOW also some bacteria can form
extensive complex internal membrane systems
- Ex. The bacterium Gemmata obscurigkobus, which forma a variety of complex internal membranes
o However, 3D reconstructions of this bacterium show these membranes do not form closed
compartments like eukaryotic organelles
o Hence, key step in producing the FECA was not formation of internal membranes itself BUT the further
development of these membranes into close internal compartments, particularly a compartment
surrounding the DNA to produce a nucleus
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Endosymbiosis model
So we have this original prokaryotic cells which are relatively primitive (earliest ones). Many of these are heterotrophs
eaig that the ae ells that ee’t apale of fiig aos, the had to atuall osue iogai ao ase
molecules, simple molecules that were available in the environment for them.
From that we had one cell that decided to be different and develop a whole bunch of internal organization, primarily
among this is a membrane system that encloses some macromolecules capable of being the genetic material. Of course
we think that this was originally RNA, not DNA, b/c RNA has the capacities of both being the nucleic acid and catalytic
capacities just like proteins. So, we have kinda a compartment that can hold some of the information. SO the First
eukaryotic common ancestor (FECA).
- So at this step the endosymbiotic theory is taking hold, the primitive aerobic prokaryote that are now living within
the primitive eukaryotic cell in an endosymbiotic relationship, producing the mitochondria and this is thought to
e the oigial Last eukaoti oo aesto LECA BEFORE a suset of… stated to a o ee oe ad
have an endosymbiotic relationship with for ex., the cyanobacteria (the photosynthetic bacteria) to give rise to
plant cells (which ofc are diff from animal)
Textbook: A model depicting stages in the evolution of eukaryotes.
- Starting from a prokaryotic ancestor, internal compartments began to develop, leading to an organism with internal
membrane compartments such as a nucleus.
- Such an organism is known as the First Eukaryotic Common Ancestor (FECA).
- The molecular machinery for making internal membranes then allowed the FECA to engulf and maintain
endosymbiotic organisms, allowing the addition of mitochondria.
- Additional evolutionary action gave rise to cellular features common to all eukaryotic lineages, including cilia, intron
splicing, and meiosis.
- The organism that had all these traits, and therefore gave rise to all existing eukaryotic lineages, is known as the Last
Eukaryotic Common Ancestor (LECA).
- After the LECA arose, further evolutionary steps, such as endosymbiosis of photosynthetic bacteria to produce
chloroplasts, gave rise to different classes of eukaryotic cells.
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Types of prokaryotes
-2 major groups:
1. Archaea (archaebacteria)
eteophiles- thermophiles that grow @ 80-105°C (tend to live in very extreme Temperature, typically in very
high temperatures)
o Ex. Places like Yellowstone national park, in spring there archaea bacteria, lives happily in 121 degrees which is
their primary T
o The do’t like it he the tepeatue dops too uch below their primary temperature
o  degees is a speial ue eause that is the tepeatue e steilize …. euipet
Good thing the archaea bacteria are not human pathogen or will cause little trouble
2. Bacteria (eubacteria) -all other bacteria
Ex. cyanobacteria -most complex (has very complex of intercellular organization of membrane, in which those
membranes are very similar to the photosynthetic membrane that we see in plant cells)
Despite the complexity of these organisms, Archaea are actually closer to eukaryotes than eubacteria! Based on
complexity
Types of eukaryotic cells
1. Unicellular ex., protists
One cell does everything the organism needs through motile device such as the flagella and cilia
everything that this organism needs to survive is done by the one cell.
2. Multicellular ex., humans
Many Millions of cells
different activities are carried out by different types of specialized cells which is the name of the process described
on the left cell differentiation
Cell differentiation is process used through which cells produce those specialized cells
So, if we have a
fertilized human
oocyte, it would take
us about 250 cell
differentiation events
to give rise to for ex
human being.
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