Team:SDU-Denmark/project-t

From 2010.igem.org

(Difference between revisions)
(Bacterial flagellar motility 101)
(Bacterial flagellar motility 101)
Line 20: Line 20:
Different taxis pathways that steer cells towards favorable conditions and away from danger work by regulating the frequency of tumbling events.  We can take an example where a cell is getting close to a toxin it can sense and react to. As it gets closer to the source of the toxin, intracellular pathways will increase the frequency of tumbling events, in effect preventing the cell from rushing into certain doom, and since the frequency of tumling events will decrease if the cell is going in a direction away from the toxin, it will ”encourage” the cell to continue in that direction. In the case of an attractant such as an increase in nutrient concentration, the pattern will be oppisite, so that the cell is encouraged to continue towards the source of the attractant. This form of movement, combining tumbling and running, with regulation of the tumbling frequency is termed a biased random walk. <br><br>
Different taxis pathways that steer cells towards favorable conditions and away from danger work by regulating the frequency of tumbling events.  We can take an example where a cell is getting close to a toxin it can sense and react to. As it gets closer to the source of the toxin, intracellular pathways will increase the frequency of tumbling events, in effect preventing the cell from rushing into certain doom, and since the frequency of tumling events will decrease if the cell is going in a direction away from the toxin, it will ”encourage” the cell to continue in that direction. In the case of an attractant such as an increase in nutrient concentration, the pattern will be oppisite, so that the cell is encouraged to continue towards the source of the attractant. This form of movement, combining tumbling and running, with regulation of the tumbling frequency is termed a biased random walk. <br><br>
-
[[Image:Team-SDU-Denmark-Biased_random_walk.png | 400px | thumb |right]]
+
[[Image:Team-SDU-Denmark-Biased_random_walk.png | 300px | thumb |right | A biased random walk motion pattern.]]
To understand how this can work we need a simplified understanding of the chemotaxis pathway at a molecular level. Chemotactic receptors can both increase and decrease tumbling frequencies to generate biased random walk behaviour. Increased tumbling is achieved through a phosphorylation cascade beginning with the binding of a repelant to a transmembrane receptor . The receptor is linked to two proteins CheW and CheA.  CheA is a histidine-kinase that will autophosphorylate when the repelant binds. The phosphoryl group is then transfered to CheY activating the protein. The flagellar has high affinity for CheY-p, and binding reverses the mode of movement from run to tumbling. CheY-P is continuosly dephosphorylated back to CheY by CheZ which is present in the cytosol. A receptor sensing an attractant might instead switch from a default active CheA state to an inactive state when it’s ligand is bound, thus decreasing CheY phosphorylation.<br><br>
To understand how this can work we need a simplified understanding of the chemotaxis pathway at a molecular level. Chemotactic receptors can both increase and decrease tumbling frequencies to generate biased random walk behaviour. Increased tumbling is achieved through a phosphorylation cascade beginning with the binding of a repelant to a transmembrane receptor . The receptor is linked to two proteins CheW and CheA.  CheA is a histidine-kinase that will autophosphorylate when the repelant binds. The phosphoryl group is then transfered to CheY activating the protein. The flagellar has high affinity for CheY-p, and binding reverses the mode of movement from run to tumbling. CheY-P is continuosly dephosphorylated back to CheY by CheZ which is present in the cytosol. A receptor sensing an attractant might instead switch from a default active CheA state to an inactive state when it’s ligand is bound, thus decreasing CheY phosphorylation.<br><br>

Revision as of 21:54, 25 October 2010