Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 5

QUANTITATIVE Actin' Up. The polymerization of G-actin into microfilaments can be followed using pyrene-labeled actin and a device to measure the fluorescence of polymerized actin in a test tube. The increase in fluorescence can then be plotted over time, similar to using light-scattering to measure tubulin polymerization. Examine the graph in Figure 13-25, and identify which of the curves corresponds to each of the following situations. In each case, state your reasoning.

(a)Pyrene-labeled actin is added alone in the presence of buffer.
(b)Pyrene-labeled actin is added along with purified Arp2/3 complex proteins and a purified protein fragment that corresponds to active N-WASP (a WASP family protein).