398 9.2  Systems Biology and Biophysics: “Systems Biophysics”

elucidating characteristics of the key molecular components in their original biological con­

text (see Chapter 7).

The range of signals detected by bacteria is enormous, including not only nutrients but

also local oxygen concentration and the presence of toxins and fluctuations in pressure

in the immediate surroundings, but the means by which signals are detected and relayed

have strong generic features throughout. For similar reasons in studying single bacteria, we

can increase our understanding of sensory networks in far more complicated multicellular

FIGURE 9.1  Systems biophysics of cell chemotaxis. (a) A multicellular slime mold body of

species Dictyostelium discoideum indicating movement of the whole body (gray) in the direc­

tion of a chemoattractant gradient, which results in a redistribution of chemoattractant receptor

complexes (circles) in the cell membrane after perturbing the chemoattractant concentration

gradient (right panel). (b) Schematic indicating the different protein components that comprise

the bacterial chemotaxis pathway in Escherichia coli, which results in a change in the rotational

state of the flagellar motor in response to detected concentration changes in chemoattractant

outside the cell.