1. Origin of Eukaryotic Cells

2. Prokaryotes dominated earth for about 1 by
Earth is 4.6 byo
Life originated 3.5–4.0 bya
Prokaryotes dominated earth for about 1 by 2

3. Cyanobacterium heterocyst
Cyanobacteria
Cyanobacterium heterocyst
A type of prokaryote with much infolding of the cell membrane
Capable of performing photosynthesis, which releases oxygen into the atmosphere 3

4. Oxygen atmosphere Oxygen begins to accumulate 2.7 bya
evidence in banded iron in rocks (rusting)
makes aerobic respiration possible 4

5. Eukaryotes
Nearly all are aerobic,
they depend on free oxygen to carry out their metabolic processes
Accordingly, they could not have evolved before at least some free oxygen was present in the atmosphere

6. Two processes are thought to have led to the origin of eukaryotes….
Infoldings of the prokaryotic cell membrane
Endosymbiosis

7. Development of internal membranes
create internal micro-environments (“compartments”)
advantage = increase efficiency
~2 bya
nuclear envelope
*note double membrane
endoplasmic reticulum (ER)
plasma
membrane
infolding of the plasma membrane
nucleus
DNA
cell wall
plasma
membrane
Prokaryotic ancestor of eukaryotic cells
Prokaryotic
cell
Eukaryotic
cell

8. Given what you know about in folding and the cell membrane as a phospholipid bilayer:
Why is the nuclear membrane a DOUBLE membrane (two layers of bilayer)

9. Infoldings of the prokaryotic cell membrane
REMEMBER: Two processes are thought to have led to the origin of eukaryotes….
Infoldings of the prokaryotic cell membrane
Endosymbiosis

10. internal membrane system
Endosymbiosis
FIRST early eukaryotic cells engulfed aerobic bacteria but did not digest them
Led to the origin of mitochondria
Mutually beneficial relationship
internal membrane system
aerobic bacterium
mitochondrion
Endosymbiosis
Ancestral
eukaryotic cell
Eukaryotic cell
with mitochondrion

11. chloroplast & mitochondrion
Endosymbiosis
Eukaryotic
cell with
mitochondrion
THEN early eukaryotic cells engulfed photosynthetic bacteria but did not digest them
Led to origin of chloroplasts
(mutually beneficial relationship)
chloroplast
mitochondrion
Endosymbiosis
Eukaryotic cell with
chloroplast & mitochondrion

12. Endosymbiosis
In this relationship one cell lives within the other, which is a special type of symbiosis called endosymbiosis.
In some cases of a symbiotic relationship, one symbiont cannot live independently of the other.
This may have been the case early symbiotic prokaryotes that became increasingly interdependent until the unit could exist only as a whole.

13. A model of the origin of eukaryotes

14. Theory of Endosymbiosis
Lynn Margulis
How is the word “theory” in science different than the use of the word theory in every day language?

15. Structural Evidence Resemble bacterial structure
Both mitochondria & chloroplasts
Resemble bacterial structure
Are found in membranous envelopes (like a cell membrane)
are the same approximate size as prokaryotes
have 70s ribosomes

16. Genetic Evidence have circular naked DNA
Both mitochondria & chloroplasts
have circular naked DNA
DNA shares common sequences with modern prokaryotes

17. move freely within the cell
Functional Evidence
Both mitochondria & chloroplasts
move freely within the cell
reproduce independently from the cell through binary fission
are inhibited by antibiotics

18. Where Did Organelles Come From ?
Membranous infoldings
Nucleus ER
Golgi
Lysosomes
Vesicles
Endosymbiosis
Mitochondria
Chloroplasts

19. Membrane infolding
Endosymbiotic theory