BIO130H1 Lecture Notes - Lecture 18: Myosin, Dynein, Hydrolysis
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They are made of monomers but they are polar, which means that the ends are different. Polar bonds = one side is more positive and one side is more negative. One end is n terminus while the other end is c terminus. The n"s and the c"s are the plus end. 13 parallel proto filaments to form a hollow cylinder. Myosin ii, plus end is directed to compare the different functions: ensure to compare their different motor proteins. 0 = all the actin is monomers. 100 = no monomers all in the actin form the addition of the salt to make a buffer, the addition of the salt changes the conformation from actin monomers to filaments. Actin length is growing, addition at the plus end is faster. Eventually an equilibrium state will be achieved where the addition will be equaled with the loss.
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Activity: Dynamic Instability of Microtubules
Part A
What causes catastrophe of the microtubule in vitro?
the lack of tubulin heterodimers |
non-motor Microtubule Associated Proteins (MAPs) |
GTP hydrolysis |
mutation of the β-tubulin |
Part B
What is the role of GTP in microtubule polymerization?
GTP binds the alpha and beta tubulin subunits together to form the tubulin monomer. |
GTP hydrolysis provides the energy for the polymerization of the microtubule. |
GTP is a second messenger that signals the need for polymerization/de-polymerization. |
GTP stabilizes the tip of the microtubule, allowing more monomers to be added. |
Part C
What would happen in the treadmilling experiment if a non-hydrolyzable analogue of GTP were used?
The monomers would be unable to add to the plus end, and the microtubules would shrink until they disappeared. |
The microtubule would treadmill until the new tubulin, with non-hydrolyzable GTP, reached the minus end, and then it would only extend at the plus end. |
The microtubule would add monomers at both the plus and minus ends, growing in both directions. |
The non-hydrolyzable GTP would stabilize both ends, causing treadmilling to stop. |
Part D
What is the difference between the plus and minus ends of the microtubule in in vitro experiments?
The beta subunit of the tubulin is exposed on the minus end. |
Polymerization occurs at the plus end. |
The plus end has a lower critical concentration for tubulin heterodimers. |
Catastrophe occurs at the minus end. |
Part E
How would the drug taxol affect the in vitro dynamic instability and treadmilling experiments?
Taxol would block catastrophe at the plus end in the dynamic instability experiment but not depolymerization at the minus end in the treadmilling experiment. |
Taxol would block the addition of tubulin in both experiments, leading to a destruction of the microtubules. |
Taxol would stabilize the microtubules in both experiments, leading to polymerization without catastrophe. |
Taxol would block depolymerization at the minus end in the treadmilling experiment but not catastrophe at the plus end in the dynamic instability experiment. |