1. The Dawning of Eukaryotes
How Our Cells Came to Be

2. Organism with membrane- bound organelles – most notably a nucleus
What is a Eukaryote?
Organism with membrane- bound organelles – most notably a nucleus

3. Where did the Nucleus come from?
We’re really not sure.
A couple of main theories

4. 1. An Archaean invading a Bacterium
Archaeans share many genetic features with eukaryotes
Bacteria show some structural similarities to eukaryotes

5. 2. A bacterium evolved
A species of bacterium (planctomycetes) have primitive internal organelles
Maybe a relative of this species evolved more complex internal membranes?

6. 3. A virus invaded a primitive cell
Explains linear chromosomes
Some algae can infect hosts with a copy of their nucleus
Could explain all life forms, eukaryotes just had a more complex cell that was invaded

7. 4. A simple cell evolved an extra outside membrane
The original cell became the nucleus
Nuclear pores evolved that let ribosomes out of the nucleus and into the cell (ribosomes are made in the nucleus)

8. Mitochondria and Chloroplasts
We have a better idea of how they came to be by endosymbiosis
This could have happened before or after the formation of the nucleus

9. Endosymbiosis Mitochondria and chloroplasts were free living bacteria
There are bacteria capable photosynthesis/aerobic respiration
Somehow a cell took in the bacteria
They lived symbiotically together
Over time the cell came to control the mitochondria/chloroplast

10. Evidence for Endosymbiosis
Mitochondria/chloroplasts:
contain their own circular DNA
contain their own ribosomes (similar to bacterial ribosomes)
reproduce independently similar to binary fission
Many other metabolic and structural similarities
Some algae contain a chloroplast with a peptidoglycan containing cell wall

11. The Rest of the Organelles?
Probably evolved from pockets forming from the nuclear membrane
ER, Golgi, Lysosomes, Peroxisomes, Vacuoles etc. all can share and combine membrane

12. Advantage of Internal Organelles
Efficiency!
The cell is compartmentalized so each space has what it needs
I.e. the enzymes for aerobic respiration are concentrated in the mitochondria
Allows our cells to grow bigger, do more things and build more complex structures

13. Organelles Analogy Poster – Due Wednesday
As a group, think of an analogy for the cell. i.e. a city
Think of what in your analogy has an analogous function to each organelle (i.e. the mayor’s office is the nucleus, the power generators are the mitochondria, the solar panels are the chloroplast etc.)
Make a simple poster representing your analogy.
Focus on FUNCTION – not on appearance

14. Minimum Organelles Plant Animal Nucleus Plasma membrane Cell Wall
Ribosomes
Chloroplast
Mitochondria ER
Golgi
Vacuole
Nucleolus
Cytoskeleton
Nucleus
Plasma membrane
Ribosomes
Mitochondria
Smooth ER
Rough ER
Golgi
Lysosome
Peroxisome
Cytoskeleton
Nucleolus