Question

63. Incorporating the observation that beta-tubulin binds and hydrolyzes GTP, microtubules undergo catastrophe and rescue, describe the molecular mechanisms that account for the dynamic instability behavior of microtubules. 000 О В The cartoon to the left depicts the cross-section of a microtubule doublet as observed in the wall of a cilium. How many tubulin protofilaments are present within a primary cilium? 64. # of protofilaments = When the (+) end of microtubules are in the configuration shown to the left, they are: There are a number of microtubule organizing centers, including those listed below (A-D). For the following MTOC features described, note which MTOC(s) have the specific feature. A. Spindle Poles B. Centrosomes C. Golgi-CLASP D. Basal Bodies 66. MT emanate from gamma-tubulin ring complex A B C D 67. MT emanate from centriolar MTs A B C D 68. MTOCs contain centrioles A B C D

Answer 1

In tubulin, the unit of polymerization is a heterodimer consisting of alpha and beta tubulin. Both alpha and beta tubulin bind to nucleotide. Alpha tubulin remains GTP bound whereas beta tubulin binds to GTP and gets hydrolysed when the next heterodimer comes via the T7 loop of alpha tubulin. The T7 loop of beta tubulin does not have the catalytic residues to hydrolyse GTP in the alpha tubulin. Dynamic instability refers to the coexistence of assembly and disassembly at the ends of a microtubule. The microtubule can dynamically switch between growing and shrinking phases in this region.

66- B

67- A

68- B