Team:SDU-Denmark/project-t

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(References)
(Bacterial flagellar motility)
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Spinning in the counter-clockwise direction, the flagella will twist into a bundle in the shape of a corkscrew, and create a linear driving force [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]], propelling the cell in a straight line through the liquid. This form of movement is termed run. Spun in the clockwise direction one might then expect the cell to reverse, but this is not the case. Instead the flagellar bundle will unwind, thereby creating chaotic movement [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]] . This movement reorients the cell randomly and is termed tumbling. A cell will typically run for some time, then change it’s orientation by tumbling, and then run again [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 5]]. The direction of flagella rotation is controlled by the binding of a cytosolic protein CheY, more on which later [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]].<br><br>
Spinning in the counter-clockwise direction, the flagella will twist into a bundle in the shape of a corkscrew, and create a linear driving force [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]], propelling the cell in a straight line through the liquid. This form of movement is termed run. Spun in the clockwise direction one might then expect the cell to reverse, but this is not the case. Instead the flagellar bundle will unwind, thereby creating chaotic movement [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]] . This movement reorients the cell randomly and is termed tumbling. A cell will typically run for some time, then change it’s orientation by tumbling, and then run again [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 5]]. The direction of flagella rotation is controlled by the binding of a cytosolic protein CheY, more on which later [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]].<br><br>
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Different taxis pathways that steer cells towards favorable conditions and away from danger work by regulating the frequency of tumbling events [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 5]]. An example is when a bacterium gets close to the source of a lethal toxin, then intracellular pathways will increase the frequency of tumbling events, in effect preventing the cell from death. Since the frequency of tumbling 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 opposite, 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 [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 5]]. <br><br>
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Different taxis pathways that steer cells towards favorable conditions and away from danger work by regulating the frequency of tumbling events [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 5]]. An example is when a bacterium gets close to the source of a lethal toxin, then intracellular pathways will increase the frequency of tumbling events, in effect preventing the cell from dying. Since the frequency of tumbling 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 opposite, 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 [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 5]]. <br><br>
[[Image:Team-SDU-Denmark-Biased_random_walk.png | 300px | thumb |right | '''Figure 1:''' A biased random walk motion pattern.]] <br>
[[Image:Team-SDU-Denmark-Biased_random_walk.png | 300px | thumb |right | '''Figure 1:''' A biased random walk motion pattern.]] <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 a biased random walk behavior[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 6]]. Increased tumbling is achieved through a phosphorylation cascade beginning with the binding of a repellant to a transmembrane receptor[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]]. The receptor is linked to two proteins CheW and CheA[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]]. CheA is a histidine-kinase that will autophosphorylate when the repellant binds[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]]. The phosphoryl group is then transferred to CheY[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]]. The flagellar motor complex has high affinity for phosphorylated CheY (CheY-p), and binding reverses the mode of movement from run to tumble[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 7]]. CheY-p is continuously dephosphorylated back to CheY by CheZ[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 8]]. A receptor sensing an attractant might instead switch from the default active CheA state to an inactive state when it’s ligand is bound, thus decreasing CheY phosphorylation [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 6]].<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 a biased random walk behavior[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 6]]. Increased tumbling is achieved through a phosphorylation cascade beginning with the binding of a repellant to a transmembrane receptor[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]]. The receptor is linked to two proteins CheW and CheA[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]]. CheA is a histidine-kinase that will autophosphorylate when the repellant binds[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]]. The phosphoryl group is then transferred to CheY[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 4]]. The flagellar motor complex has high affinity for phosphorylated CheY (CheY-p), and binding reverses the mode of movement from run to tumble[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 7]]. CheY-p is continuously dephosphorylated back to CheY by CheZ[[https://2010.igem.org/Team:SDU-Denmark/project-t#References 8]]. A receptor sensing an attractant might instead switch from the default active CheA state to an inactive state when it’s ligand is bound, thus decreasing CheY phosphorylation [[https://2010.igem.org/Team:SDU-Denmark/project-t#References 6]].<br><br>

Revision as of 19:21, 26 October 2010