and Bacteria Viruses
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Some bacteria, such as E. coli, have
several flagella per cell (410
typically). These can rotate in two
ways :
Counter-clockwise rotation aligns the
flagella into a single rotating bundle,
causing the bacterium to swim in a
straight line.
Clockwise rotation breaks the flagella
bundle apart such that each flagellum
points in a different direction, causing
the bacterium to tumble in place.
The directions of rotation are given
for an observer outside the cell
looking down the flagella toward the
cell.
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Chemotaxis
A response of motile cells or organisms in which
the direction of movement is affected by the
gradient of a diffusible substance. Differs from
chemokinesis in that the gradient alters
probability of motion in one direction only, rather
than rate or frequency of random motion.
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Chemotaxis videos
http://www.metacafe.com/watch/318022/chemotaxis/
http://tw.youtube.com/watch?v=Ql7i_TLUurM
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The most important aspects in quality control of chemotaxis assays were described
by H. Harris in the 1950s. In the 1960s and 1970s, the revolution of modern cell
biology and biochemistry provided a series of novel techniques which became
available to investigate the migratory responder cells and subcellular fractions
responsible for chemotactic activity. The pioneering works of J. Adler represented a
significant turning point in understanding the whole process of intracellular signal
transduction of bacteria.[
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Outer membrane permeable lipopolysaccharide; to all small
molecules
Inner membrane cytoplasmic membrane; more restriction to
small molecules with membrane-bound receptor proteins
Periplasmic space contains peptidoglycan; soluble receptor
proteins
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periplasmic binding protein (PBP)
constitutive methyltransferase (CheR)
methyl-accepting chemotaxis proteins
(MCPs)
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Phosphorylation
Two chemotaxis
protein (CheW)
monomers and a CheA
dimer are shown
interacting with the
highly conserved
signalling domain of
the MCPs in the
cytoplasm.
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One CheA monomer will
probably not interact with one
MCP dimer, and instead a
CheA dimer might span
several receptors. A decrease
in attractant concentration
induces transautophosphorylation of the
CheA dimer, which
phosphorylates the response
regulator CheY.
Phosphorylated CheY then
binds to the flagellar motor to
bring about a change in
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direction.
Methylation
Receptor Clusters
Phosphorylated CheA also
phosphorylates another response
regulator the methylesterase CheB.
Phosphorylated CheB competes with a
constitutive methyltransferase, CheR, to
control the degree of methylation of
specific glutamates in the MCPs.
This resets the signalling state of the
receptors and allows them to adapt to
the present concentration of attractant
and to sense subsequent changes.
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Behavior of an
organism
explained at
molecular level
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