Chemotaxis: a physiological adapation |
A dramatic example of rapid adaptation is the process of "chemotaxis", i.e. the ability to move toward nutrients (positive chemotaxis) and away from noxious compounds (negative chemotaxis). This is a valuable trait in bacteria, since it enages them to swim to sources of nutrients and away from toxic chemicals. Chemotactic responses are very rapid, they do not require active gene expression. How is it that bacteria move directionally? One way that some types of bacteria move involves organelles known as flagella. These are rotary motors powered by ion gradients across the plasma membrane. This motor drives a helical propeller. The basic motor can rotate in either a clockwise or a counterclockwise wise direction. |
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There are two possible ways to do this. One would be to measure the difference in concentration between the two ends of the bacterium. This is difficult, since the bacteria is very small (1-2 um long) and the differences in concentration between two points separated by 1-2 um is very small (perhaps we could calculate this?) An alternative approach is to measure the concentration around the bacteria as a function of time. If it is increasing, the bacteria is moving toward the source of the chemical; if it is decreasing, it is moving away from thge source. |
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Use Wikipedia |
19 March 2005 revised 21-Mar-2013
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