Introduction
Abiogenesis
Explains how cells came from non-living materials through abiogenic synthesis. Accumulation of organic compounds was possible when the Earth contained no O2. Simple non-living organic molecules got increasingly complex until they formed early life of prokaryotes.
Who demonstrated Abiogenesis
Miller and Urey
(2.45BYA) The Great Oxygenation event
Caused the first mass extinction of anaerobic cells as O2 was toxic. Cyanobacteria produced O2 doing photosynthesis, oxygen accumulated in the earth after we had not enough iron rock for the O2 to dissolve in.
+(450MYA) The Ordovician mass extinction
Gamma rays bursting from a nearby Hypernova in the Milky Way galaxy damaged the Ozone layer, causing rapid glaciation since Nitrogen and Ozone reacted to form nitrogen dioxide.
(250MYA) Permian Triassic extinction event
Eruptions of volcanos that took 2 million years extinguished about 95% of marines and 75% of land animals. It took 30 million years to recover the vertebrates.
(65MYA) The Cretaceous Paleogene
Asteroid caused 3/4 of organisms to die. Ecothermic species who were up to 25kg best survived.
How did cells get constructed?
Earth's early atmosphere:
Lacked molecular oxygen (O2), allowing interactions between hydrogen and carbon
These interactions led to the formation of various organic molecules through prebiotic or abiogenic synthesis.
Chemical complexity increases:
As chemical reactions diversified, certain molecules (believed to be RNA) emerged with the ability to control their own biochemical reactions and replication.
This "RNA world" stage saw RNA molecules replicating themselves, followed by the development of protein synthesis and later, DNA.
The rise of photosynthesis:
The first photosynthesizing prokaryotes utilized hydrogen sulfide (H2S) and converted it to sulfur
Cyanobacteria later evolved, using water (H2O) as a source and releasing oxygen (O2) – leading to the Great Oxygenation Event.
Structure of Prokaryotic Cells:
Size and Shape:
Tiny, measuring 1-10 micrometers in diameter.
Can be spherical, rod-shaped, or spiral-shaped.
Basic Components:
Cell membrane:→Made of lipids and protects the cell.
Nucleoid: Central region containing the bacterial chromosome (DNA).
Cytoplasm: Filled with ribosomes for protein synthesis and contains DNA plasmids.
Cell wall: Made of polysaccharides and provides structural support.
Capsule (optional): Additional protective layer outside the cell wall.
Flagella (optional): Hair-like structures for movement.
Spores (optional):
Dormant structures formed under harsh conditions.
Model Organism:
Escherichia coli (E. coli): Most commonly used model organism for studying prokaryotes.
Prokaryotic Cell Division:
Binary fission: Asexual reproduction where one cell divides into two identical daughter cells.