Download Eukaryotic Origins

The Dawning
of Eukaryotes
How Our Cells Came to Be
What is a Eukaryote?
Organism with
membranebound
organelles –
most notably a
nucleus
Where did the Nucleus come from?
We’re really not
sure.
A couple of main
theories
1. An Archaean invading a Bacterium
Archaeans share
many genetic
features with
eukaryotes
Bacteria show
some structural
similarities to
eukaryotes
2. A bacterium evolved
 A species of bacterium (planctomycetes) have
primitive internal organelles
 Maybe a relative of this species evolved more
complex internal membranes?
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
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)
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
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
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
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
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
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
Minimum Organelles
Plant
Animal

Nucleus

Nucleus

Plasma membrane

Plasma membrane

Cell Wall

Ribosomes

Ribosomes

Mitochondria

Chloroplast

Smooth ER

Mitochondria

Rough ER

ER

Golgi

Golgi

Lysosome

Vacuole

Peroxisome

Nucleolus

Cytoskeleton

Cytoskeleton

Nucleolus