cellular theory and evolution

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