Question

6. Graph on the right shows the time course of the polymerization of pure tubulin in vitro. Three parts of the curve are labeled above it as A, B, and C. You conduct a similar in vitro tubulin-polymerization experiment, only you include purified centrosomes in your preparation. When you plot your data, which part of your graph should be most dissimilar to the curve shown in the graph? a. A b. B c. C d. A and C e. None. The shape of my graph should be identical to the graph produced when tubulin is polymerized in the absence of purified centrosomes. percentage of tubulin molecules in microtubules time at 37°C

Answer 1

Answer is A (part A of the graph will be most dissimilar)

Centrosomes contain the protein gamma tubulin which forms the gamma tubulin ring complex in centrosomes, and that acts as a nucleation center for tubulin polymerization. The gamma tubulin acts as a scaffold and thereby speeds up the process of tubulin polymerization. So in presence of centrosomes, the initial lag phase of tubulin polymerization will not be observed in the graph, and tubulin will polymerize at a high rate right from the beginning. Hence part A of the graph will be absent.