Cellular Theory and Evolution
The Cell Theory
1.
2.
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All cells come from pre-existing cells
(Virchow)
All plants and animals are composed of cells
(Schleidan and Schwann)
Now with more microscopic knowledge of the
other three kindgoms, we can say that cells
are the fundamental units life.
Cellular Evolution
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
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The original cellular life was heterotrophic and
prokaryotic. (Monera)
Then, cells became larger and through
endosymbiosis incorporated the mitochondrion
and chloroplast. (Protista)
Finally, cells joined to form multicellular
organisms. (Plantae, Animalia, Fungi)
Prokaryotic Characteristics
1.
2.
3.
4.
5.
6.
7.
8.
9.
Single circular chromosome
Plasma membrane but no nuclear membrane
Energy production is a function of the cell
Featureless cytoplasm
No permanent cytoskeleton
Cell wall of peptidoglycan (amino acid/sugar)
No endosymbionts
Metabolic diversity
Intracellular transport relies on diffusion
Eukaryotic Characteristics
1.
2.
3.
4.
5.
6.
Large in size (volume 1000 >than prokaryote)
Energy production function of organelles
Cytomembrane system
Organelles of movement
Larger genome, with interrupted genes, noncoding regions of DNA
Cytoskeleton integrated with membrane and
cytoplasm
CELLULAR
SIGNAL TRANSDUCTION
The bacterial flagella
Flagella Motor: Clockwise
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
Spins Counter Clockwise
Multiple flagella spiral into a single tail causing the
bacteria to move in a straight line
Flagella Motor: Counter Clockwise
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
Spins Clockwise
The flagella unfurl and
stroke independently
causing the bacteria to
move more randomly
Movement in the Environment

By adjusting the proportion of the two types of
movement described, a bacterium can direct
itself in its environment
Bacterial Senses: Receptors


The Escherichia coli has
five protein membrane
receptors that bind
particular receptors
important to their life.
One example is the Tar
Receptor which binds
the amino acid
“aspartate”.
The Tar Receptor
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

The Tar receptor has two functional
components.
The sensory binding site for aspartate lies
outside the inner membrane.
The receptor spans the membrane with a
mobile helical segment lying in the cytoplasm
acting as a swinging piston.
Intracellular Communication
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
The swinging piston prompts Chemotaxis
(Che) W to activate the kinase CheA.
CheA transfers a phosphate group to CheY,
which causes the flagella rotor to change to
spinning clockwise
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Flagella Assembly
Flagella Reversal
Flagella Experiment
Bibliography
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Debra Niehoff (2005) The Language of Life:
How Cells Communicate in Health and
Disease, Joseph Henry Press, Washington,
D.C.
Protonic Nanomachine Project & The
Laboratories for Nanobiology (Information)
Flagella and ID Websites