10-17 - BIO 5099: Molecular Biology for Computer Scientists...

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BIO 5099: Molecular Biology for Computer Scientists (et al) Lecture 15: Some Prokaryotic loose ends and the origin of the Eukaryotes http://compbio.uchsc.edu/hunter/bio5099 Larry.Hunter@uchsc.edu A few more tidbits on Bacteria Sensation, Awareness and Action (and the precursors to metazoan signaling systems) Bacterial sex Horizontal transmission of genes (no, not lying down!) There are no living fossils Bacteria are contemporary organisms, not ancient ones. Taxes Taxis (plural taxes) is a movement of an entire organism in response to stimuli Chemotaxis: chemical stimulant (food, oxygen, toxins) Phototaxis: light Magnetotaxis: magnetic field (direction) Chemotaxis to sugar Phototaxis Magnetotaxic bug
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Organism must Sense the direction of the stimuli Be able to control the direction of movement Set the direction of movement to follow (or avoid) the stimulus Prokaryotes can do this. How? Receptors sensitive to changes in stimulus Cytoplasmic signaling mechanism that transduces information from receptor to effector The flagellum (motor) and a modest sort of directional control Sensing proteins Methyl-accepting chemotaxis proteins (MCPs) are membrane- bound receptors. There are various kinds of MCP for different ligands. Part of the receptor is in the periplasm (between cell membrane and cell wall), part inside the cytoplasm Also has a “transmembrane region” Cytoplasmic side has many methylatable glutamate residues Adaptation An increase in ligand concentration causes chemotactic effects for only a few minutes. Ligand binding to MCP has two effects: Rapidly decreases the activities of two proteins that bind to the cytoplasmic receptor (CheA and CheY), which forms the basis for the signal to the flagellar “motor” If the binding lasts long enough, it will slowly increase the likelihood that the MCP will be methylated. MCP can be methylated with as many as 8 methyl groups.
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10-17 - BIO 5099: Molecular Biology for Computer Scientists...

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