Figure 15-67. The sequential activation and adaptation (via methylation) of a chemotaxis receptor.

Figure 15-67The sequential activation and adaptation (via methylation) of a chemotaxis receptor

Note that the activity of the receptor, and there-fore the tumbling frequency of the bacterium, is the same in the resting and adapted states. The receptor is shown with two methylation sites for simplicity; in fact, there are eight on each receptor. As the concentration of attractant increases, the fraction of time that the receptor is occupied by the attractant increases. A higher level of attractant will thereby initially cause a greater change in the conformation of the receptor than a low level, pushing the receptor more toward its fully inactivated state. An increase in methylation ensues, however, so that within minutes the conformational strain on the receptor is exactly reversed, and the activity of the receptor increases to its previous level. The receptor has now adapted.

From: Target-Cell Adaptation

Cover of Molecular Biology of the Cell
Molecular Biology of the Cell. 3rd edition.
Alberts B, Bray D, Lewis J, et al.
New York: Garland Science; 1994.
Copyright © 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D Watson.

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