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1.1  Motivation for Biophysics

individual scattering components. This tight coupling in the life sciences between analytical

and experimental physical science tools is far from unique; rather, it is a general rule.

But, paradoxically, a key challenge for modern biophysics has been, in the same manner

in which it is difficult for the child to emerge from the shadows of an achieving parent, to

break free from the enormous successes made through the application of structural biology

methods, in particular, over half a century ago. Structural biology, in its ability to render

atomic level detail of the molecular machinery of living organisms, has led to enormous

insight in our understanding of the way that biological molecules operate and interact with

each other. However, what structural biology in its existing form cannot offer is any direct

information about the dynamic process in living cells. This is a core weakness since bio­

logical processes are anything but static. Everything in biology is dynamic; it is just a matter

of over what time scale. However, dynamic processes are something that single-​molecule

FIGURE 1.1  Hodgkin–​Huxley model of membrane current in the nerve. (a) Typical ion channel in a nerve cell membrane.

(b) The action of ion channels in the membrane results in a spikelike response in the measured membrane voltage. A single-​

ion channel in a cell membrane can be modeled (c) as a resistor–​capacitor electrical circuit, which (d) can be generalized

to account for different types of ion flow across the membrane including sodium (Na^+​) and potassium ions (K^+​), plus the

effects of any other types.