Need help with 5a please! pts) What happens during the stages o dynamic instabil
ID: 205170 • Letter: N
Question
Need help with 5a please! pts) What happens during the stages o dynamic instability in microtubules, and what triggers the change between one stage to the next? (2pts) Suppose a microtubule severing protein breaks microtubules in half, forming two microtubules of shorter length. Do you predict that the newly exposed microtubule plus ends will grow or shrink? Please explain your answer. B. C. (2pts) Suppose you grow microtubules with mutant tubulin subunits that are unable to hydrolyze GTP. Do you expect to see dynamic instability in these microtubules? Please explain your answer.Explanation / Answer
5a.
Microtubule is formed by the lateral association of thirteen protofilaments. The protofilaments are made up of alpha and beta tubulin dimers. Microtubules are long, hollow and cylindrical with a minus end and a plus end. The dynamic properties of growth and shrinkage occurs at the plus end of microtubule.
Dynamic instability: The co-existence of growing and shrinking microtubules in the same conditions is termed dynamic instability.
Whether microtubules are growing or shrinking depends uopn the rate of GTP hydrolysis. GTP-bound protofilaments assembly would result in a flat sheet-like lattice of tubulin protofilaments. Assembly into the final cylindrical conformation is dependent upon GTP hydrolysis. In their stable state microtubles are predominately composed of GDP-bound -tubulin protofilaments.
One important point is that the rate of assembly often outpace the rate of hydrolysis due to which a GTP-cap is produced which effectively constrains the curvature of the protofilaments. When hydrolysis catches up at the tip of the microtubule, the constraint is removed and the protofilaments become highly unstable. This results in rapid depolymerization and shrinkage. This switch from growth to shrinking is called a catastrophe. GTP-bound tubulin units can begin adding to the tip of the microtubule again, providing a new cap and protecting the microtubule from shrinking. This is referred to as "rescue".