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Cellular Theory and Evolution
The Cell Theory
1. All cells come from pre-existing cells (Virchow)
2. 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
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. Single circular chromosome2. Plasma membrane but no nuclear membrane3. Energy production is a function of the cell4. Featureless cytoplasm5. No permanent cytoskeleton6. Cell wall of peptidoglycan (amino acid/sugar)7. No endosymbionts8. Metabolic diversity9. Intracellular transport relies on diffusion
Eukaryotic Characteristics
1. Large in size (volume 1000 >than prokaryote)2. Energy production function of organelles3. Cytomembrane system4. Organelles of movement5. Larger genome, with interrupted genes, non-
coding regions of DNA6. Cytoskeleton integrated with membrane and
cytoplasm
CELLULARSIGNAL TRANSDUCTION
The bacterial flagella
Flagella Motor: Clockwise
Spins Counter Clockwise Multiple flagella spiral into a single tail causing the
bacteria to move in a straight line
Flagella Motor: Counter Clockwise
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
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
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
Flagella Assembly Flagella Reversal Flagella Experiment
Bibliography
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