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Formation of Prokaryotes
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Lecture notes about prokaryotes from first year
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Lecture 1: How prokaryotes evolvedFirst great diversification: prokaryotes and 2 domains.. All major metabolic pathways developed.
They started to compete and eventually became extinct. Early prokaryotes were anaerobic and
chemoheterotrophic. They were faced with constantly changing physical and biological movements.
All of the major metabolic capabilities of prokaryotes, including photosynthesis, probably evolved in
the first billion years of life. This happened 2.7 b years ago.
Once photosynthesis occurred, it released a huge amount of oxygen into the atmosphere, which
then reacted in the atmosphere to form ozone. This formed an ozone layer which protected the
surface of the earth from UV radiation. Cyanobacteria existed 2.7 billion years ago. Evidence of
photosynthesis and oxygen liberation is from 3.5 b years ag from rust deposits of oceans.
Today, the collective biomass of prokaryotes outweighs all eukaryotes combined by at least tenfold.
Most prokaryotes are unicellular, although the cells of some species remain attached after cell
division. There are 2 prokaryotic domains: bacteria and archaea. Prokaryotes grow by nuclear fission.
Some may aggregate transiently or form true colonies. Most common shapes are cocci (spherical),
bacilli (rod shaped) and spiral.
Key features of prokaryotes:
They have cell walls which maintains the shape and protects the cell, prevents bursting in a
hypotonic env. Most bacterial cell walls are made of peptidoglycan (diff to eukaryotic cell walls) but
archaeal cell walls lack this.
Using a technique called gram stain, scientists can categorize many bacterial species according to diff
in cell wall composition. Gram positive bacteria have simpler walls made of a thick layer of pep.
Gram-negative is the opposite.
Cell adhesion, as they must stick together. Cells communication. Dependency as cells must depend
on surrounding cells for survival, otherwise the body is just a large colony. Differentiation: the cells
of the body differentiate at diff tasks (mostly permanent).
Many prokaryotes are capable of directional movement.
There are differences in the structure of the flagella in pro and euk. The action of the flagella is the
most common method of movement.
Prokaryotic cells lack a nucleus enclosed by membranes. Includes plasmids. Also lacks membrane
bound organelles. Only half of the flagellums protein components are necessary for it to function.
Flagella may be scattered over the entire surface of the cell or concentrated at one or both ends.
They're not covered by an extension of the plasma membrane.
The prokaryotes chromosome is located in the nucleoid (a region of cytoplasm that’s not enclosed
by a membrane)
Archaea are considered to live in extreme environments (mostly). They have least as much in
common with euk and bacteria. They also have many unique characteristic.
Viruses can't reproduce on their own. They evolved after cells.
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