Chemistry Reference
In-Depth Information
Figure 13.2 Two modes of single-molecule force
spectroscopy. (A) A simplified diagram of the
AFM, showing the laser beam reflecting on the
cantilever, to a photodiode detector. The
photodiode signal is calibrated in picoNewtons
of force. A polyprotein is pulled at constant
velocity by means of a piezoelectric actuator the
increasing pulling force triggers the unfolding of
a module. Continued pulling repeats the cycle
resulting in a force-extension curve (B) with a
characteristic sawtooth pattern. (C) When
pulling is done under feedback, the piezoelectric
actuator abruptly adjusts the extension of the
polyprotein to keep the pulling force at a constant
value (force-clamp). Unfolding now results in a
staircase-like elongation of the protein as a
function of time.
