Question

AMP-PNP is the abbreviation for a structural analogue of ATP in which the second and third phosphate groups are linked by an NH group (instead of an oxygen atom). AMP- PNP can bind to the ATP-binding site of most ATPases. It differs from ATP in that the
terminal phosphate cannot be removed by hydrolysis (so you cannot create ADP, therefore, you cannot get energy from AMP-PNP). Based on this information, explain the following

a. When isolated myofibrils are placed in a flask containing Ca2+ and AMP-PNP, contraction is quickly arrested. Where in the contraction cycle will contraction stop? Be specific.
b. What affects would you predict for cilia on a paramecium to which AMP-PNP is added? Be specific as to the proteins / molecules whose function would be inhibited and what would be the overall affect?
c. When researchers incubated purified vesicles, axoplasm (containing motor proteins), and MT from the giant squid axon and added AMP-PNP, the vesicles did not move along the MT. Explain this observation using specific proteins / processes affected.

Answer 1

Answer:

Explanation:

a.

Actin and myosin, two contractile proteins, make up myofibrils. ATPase activity is present in the myosin head. Troponin tropomyosin complex is displaced by calcium ions, exposing myosin's entire surrounding binding site on actin. Myosin heads execute the power stroke, and detachment of the head is needed for the second cycle. Myosin head detachment is aided by ATP binding & hydrolysis. Since the solution contains AMP-PNP instead of ATP, myosin heads are unable to hydrolyze and detach from myosin-binding sites on actin, thereby preventing contraction.

b.

The active ATPase correlated with both the dynein arms is found in cilia and flagella. Dynein is a motion motor protein family that walks around microtubules. The core of cilia is made up of microtubule bundles linked to the motor protein dynein. In the presence of AMP-PNP, the net reaction will be to stop the ciliary movement by inhibiting dynein motor proteins.

c.

Kinesins and Dyneins, two groups of motion motor proteins with ATPase activity, are involved in axonal transportation. All the motion motor proteins use energy from ATP hydrolysis to transfer secretory vesicles through microtubules. Since the inclusion of AMP-PNP does not supply electricity, vesicular transport does not occur.