Question

Suppose you discover a novel process in a little-studied cell type in which application of a chemical causes an unknown organelle to undergo energy-dependent movement from near the MTOC to the plasma membrane. To probe the cytoskeletal elements required for this movement you add an actin depolymerizing drug latrunculin A. This drug does not affect the initial movement of the organelle away from the MTOC, however the organelle stops before reaching the plasma membrane. You next try the microtubule depolymerizing drug colchicine. This drug prevents any movement of the organelle away from the MTOC in response the chemical stimulus.

1. What do these results tell you about the identity of the cytoskeletal elements involved and the identity of the required motor proteins over the course of movement?

2. Predict the result you would get if you added both latrunculin A and colchicine at the same time. Would the resulting phenotype be a combination of adding each drug alone, would one or the other drug’s effects predominate, or would they cancel each other out? Why?

Answer 1

Answer:

1):

• Motor proteins uses the energy from the ATP hydrolysis to bring out the movement.
• Kinesin and dynein are the motor proteins that move along the microtubules.
• Kinesin move towards the plus end whereas dynein moves towards the plus end.
• Kinesin is the main motor protein involved in movement from the center of the cell to the periphery.
• During treatment with latrunculin A causes actin to depolymerize but do not affect the kinesin thus organelle movement occurs to some extent.
• But when colchicine was incorporated, it inhibits microtubule polymerization and thus no movement.

2):

• If both latrunculin A and colchicine are incorporated, no movement of the organelle will take place.
• The resulting phenotype from the treatment of latrunculin A will be normal as it does not affect the mitosis.
• But when colchicine is given, no mitosis will occur.
• It inhibits the development of spindles as a result, chromosomes will not align on the metaphasic place and number of chromosomes will remain 4n.
• No cell division occurs.
• They both will have their effects. Latrunculin will have lesser effect compared to colchicine. But colchicine treatment is advantageous during cancer. It prevents the metastasis.

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