Transcript Eukaryote versus Prokaryote Eukaryotes

Lecture Topic: Evolutionary history of
earth
• Concept of Era's : evolutionary history
divided into eras.
– Pre-Darwinian concept, credited to Greeks
and Egyptians
– Era = A period of time marked by a
distinctive character
– Earth's age ~ 4.5 bybp
Figure: Some major episodes in the history of life
Eukaryote versus Prokaryote
• Prokaryotes are organisms, such as bacteria
that lack nuclei and other complex cell structures.
Eukaryotes share a common origin, and are
broken into archea (ancient) and true bacteria.
The name comes from the Greek, ευ, meaning
good, and κάρυον, meaning nut, in reference to
the cell nucleus.
Eukaryote versus Prokaryote
• Eukaryotes are organisms with complex cell/s
in which the genetic material is organized into
membrane bound nuclei and other organelles.
• Eukaryotes (also spelled "eucaryotes") comprise
protista (unicellular) and animals, plants and fungi
(multi-cellular).
Prokaryotes and Eukaryotes
The major similarities between the two types of
cells (prokaryote and eukaryote) are:
1. They both have DNA as their genetic material.
2. They are both membrane bound.
3. They both have ribosomes.
4. They have similar basic metabolism.
5. They are both amazingly diverse in forms.
Major differences between
Prokaryotes and Eukaryotes
• The major and extremely significant difference
between prokaryotes and eukaryotes is that
eukaryotes have a nucleus and membrane-bound
organelles, while prokaryotes do not.
• The DNA of prokaryotes floats freely around the cell.
• The DNA of eukaryotes is held within its nucleus.
The organelles of eukaryotes allow them to exhibit
much higher levels of intracellular division of labor
than is possible in prokaryotic cells.
Figure: Comparing the sizes of a virus, a bacterium, and a eukaryotic cell
Additional differences between
prokaryotes & eukaryotes:
Size
Eukaryotic cells are, on average, ten times the size of
prokaryotic cells.
Genomic composition and length
The DNA of eukaryotes is much more complex and therefore
much more extensive than the DNA of prokaryotes.
Cell Wall
Prokaryotes have a cell wall composed of peptidoglycan, a
single large polymer of amino acids and sugar.
Many types of eukaryotic cells also have cell walls, but none
made of peptidoglycan.
Turn to Geological Time Scale now…
History of the Earth
GEOLOGICAL TIME SCALE
ERA
PERIOD
ABSOLUTE TIME (mybp)
RELATIVE TIME*
----------------------------------------------------------------0------------------------------- 31 Dec midnight
Neogene
CENOZOIC
-------------------------------------24------------------------------ 30 Dec 1:00 am
Paleogene
------------------------------------------------------------------------------65------------------------------- 26 Dec 6:00 pm
Cretaceous
---------------------------------144------------------------------- 20 Dec noon
MESOZOIC
Jurassic
--------------------------------213----------------------------- 14 Dec evening
Triassic
---------------------------------------------------------------------------248----------------------------- 11 Dec night
Permian
PALEOZOIC
--------------------------------286----------------------------- 7 Dec evening
Carboniferous
---------------------------------360----------------------------- 2 Dec evening
Devonian
--------------------------------408----------------------------- 29 Nov night
Silurian
--------------------------------438----------------------------- 26 Nov noon
Ordovician
-----------------------------------505----------------------------- 21 Nov midnight
Cambrian
------------------------------------------------------------------------590------------------------------ 14 Nov morning
Proterozoic
PRE - ----------------------------------------------------------------2500---------------------------- 11 June
CAMBRIAN
Archean
---------------------------- -------------------------------------------4500----------------------------- 1 Jan
* Relative time is an artificial compression of the Earth’s 4.5 billion year history into a single year to facilitate an understanding of the tremendous
time periods involved since the Earth first formed.
Archean Era ~ Origin of Life
• Life appears about 3.5-4 bybp.
• Formation of continental land masses we know
today.
• First fossils - small cells, bacteria like organisms
• Most interesting changes occurred in shallow
marine habitat (many fossils preserved).
Figure A painting of early Earth showing volcanic activity and photosynthetic
prokaryotes in dense mats
Archean/Proterozoic Era:
• Evidence of ancient prokaryotes found
in S. Africa and W. Australia.
• Stromatolites = stroma ~ bed, lithos ~
rocks = banded domes of sedimentary
rock similar to layered mats formed in
salt marshes.
• Photosynthetic bacteria found in the
layers.
Figure: Bacterial mats and stromatolites
Figure: Stromatolites in Northern Canada
Figure: Early (left) and modern (right) prokaryotes
Proterozoic Era:
• Oxygen precipitates out into the ocean via iron ore
and from organisms’ metabolism.
• First Eukaryotes appear about 1.5 bybp.
• Ediacaran fauna =
• Early multicellular organisms,
• ex., algae
• All fossils present are marine
• Mass extinction of Ediacaran fauna at end of this era.
Ediacaran fauna fossil
Figure: Spheroidal Gunflint Microfossils
Figure: Filamentous cyanobacteria from the Bitter Springs Chert
Early Paleozoic Era:
Cambrian Revolution:
• First Predators seen in fossil record.
• Crawling and swimming invertebrates.
• Mass extinction end of Cambrian, followed by
radiation of many animals, such as:
– First vertebrates.
– Plants invade land along with fungi
– Another mass extinction
Middle Paleozoic Era:
•
•
•
•
Radiation of fishes.
First flightless insects.
First seed plants and trees.
Vertebrate animals invade land.
Late Paleozoic Era:
•
•
•
•
•
•
Coal swamps form great coal deposits.
Gymnosperm prominence.
Reptile prominence.
First flying insect radiation.
First terrestrial food webs.
Largest mass extinction in earth's
history, about ONE million years long.
– on average about 50% all species went
extinct.
Mesozoic Era:
• Dominant land animals radiate including,
– dinosaurs, birds, flying reptiles, crocodilians
• Mammals appear on the scene.
• Angiosperm and insect radiation
– (2nd major radiation for insects).
• Major Cretaceous Extinction: Lost dinosaurs, linked to major
cooling of earth, 65 MY ago
• How did we loose the dinosaurs?
Cenozoic Era:
• Mammalian radiation.
– First large mammals appear.
– Mammals filled niches left empty by
dinosaurs.
– Ecological Niche = reflects organisms
biotic and abiotic needs.
– Antarctica and Australia break apart.
Figure The history of continental drift
Major Points of Earth's History:
• Long history of unicellular life, multicellular life arose
relatively late, (early hot spot of activity, shallow
marine habitat).
• Modern fauna and flora arose from number of
extinctions and radiations over millions of yrs.
• Mass Extinctions follow similar pattern:
– Associated with long periods of global cooling,
followed by periods of adaptive radiations based
on new adaptive innovations, and the presence
of unfilled niches.
Figure: Diversity of life and periods of mass extinction