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How does the presence of the non-hydrolyzable GTP analogue affect cAMP-dependent receptor systems?

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Related questions

You are studying the role of dynamin in the budding and pinching off mechanism of clathrin coated vesicles from the plasma membrane. You know that dynamin uses GTP hydrolysis to perform its function, but you would like to test how dynamin behaves in the presence of a non-hydrolyzable analog of GTP. Describe an experiment that allows you to observe the function of dynamin in the presence of either GTP or a non-hyrolyzable GTP analog. What do you predict will happen in the presence of the analog (Be detailed in your response)?

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.

Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. Remember, the activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane. Which of the following would enhance this effect of the acetylcholine?

(a) addition of a high concentration of a non-hydrolyzable analog of GTP

(b) addition of a drug that prevents the α subunit from exchanging GDP for GTP

(c) mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine

(d) mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein

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