Wednesday, October 14, 2009

motor proteins

10.14.09. Kinesin is a well-studied example of a "motor protein," a protein that steps along microtubules to transport cargo from one side of a cell to another (see an animation of kinesin by the Vale lab at UCSF here). Recent experiments (the plot shown is from Visscher et al, Nature, 1999) have been able to track the movement of a single kinesin molecule by attaching its cargo end to a plastic bead whose displacement is controlled by a laser beam (a so-called "optical trap"). At low (or no) cargo load, the velocity of kinesin depends on two parameters: its step size and the diffusion constant. Students practiced turning statements into equations by translating sentences such as "kinesin’s velocity is the quotient of twice the diffusion constant and the step size." Students then calculated the velocity for the approximate values D = 600 nm^2/s for the diffusion constant and L = 8 nm for the step size and compared with the slope of the plot.