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Microtubule Assembly

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1. What is the main objective of this paper?

2. What is the main concept the authors are trying to explain in the introduction?

3. The authors talk about a 6S protein (the tubulin dimers) and a 36S protein (the ring structures). What does the S represent in the 6S and 36S and what is the experiment (in general terms) that yields the S notation? (This question might take some time to find the answer, but the answer can be found).

4. On page 1859, the first experiment the authors conducted was experiment using radiolabeled (radioactive sulfur [35S] and radioactive hydrogen [3H]) 6S and depolymerized microtubules. What was the goal of this experiment and what did they conclude?

5. In the second experiment explained in the results section (page 1859) the researchers did a similar experiment to the first experiment. What was the purpose of using salt in this experiment? What did the researchers discover? Why are the findings important?

6. In Table 1, on page 1860, the results showed no microtubule assembly in the presence of trypsin. In the text, the researchers state that because of this result the tau factor must be a protein. Why did the authors conclude the protein status of ? What is trypsin? What is its mode of action?

7. As an extension to question 6, are there any other chemicals that you would add to the list in Table 1? Explain your answer. What would be the results of using the chemicals you suggest?

8. This paper was written in 1975, please speculate as to what the tau factor might be known as today. Why?

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1. WHAT IS THE MAIN OBJECTIVE OF THIS PAPER?

To demonstrate that tau protein is essential for microtubule assembly in vitro.

2. WHAT IS THE MAIN CONCEPT THE AUTHORS ARE TRYING TO EXPLAIN IN THE INTRODUCTION?

The authors present background information about the physical and biochemical characteristics of microtubules. This includes their molecular dimensions and subunit composition. The authors also discuss the ubiquitous presence of microtubules in animals and plants. A number of examples are given where microtubule assembly is regulated and suggests an underlying mechanism controls microtubule polymerization in vivo. The paper points out current protocols for purifying tubulin and testing its properties in vitro provide a solid experimental system for studying the regulation of microtubule assembly. The introduction concludes with the paper's major findings; that a salt dissociable factor that makes up the 36S microtubule species is essential for microtubule polymerization and speculates that this protein plays a major role in vivo.

3. THE AUTHORS TALK ABOUT A 6S PROTEIN (THE TUBULIN DIMERS) AND A 36S PROTEIN (THE RING STRUCTURES). WHAT DOES THE S REPRESENT IN THE 6S AND 36S AND WHAT IS THE ...

Solution Summary

This solution provides an analysis of Weingarten's original paper "A protein factor essential for microtubule assembly" that was published in the Proceedings of the National Academy of Science in 1975 (Vol 72, pp 1858-62). From the current knowledge on microtubule assembly to interpretation of the results including experimental recommendations are included.

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Explanation of why two different drugs are toxic to dividing cells in regards to microtubule dynamics.

The drug taxol, extracted from the bark of yew trees, has the opposite effect of the drug colchicine, an alkaloid from autumn crocus. Taxol binds tightly to microtubules and stabilizes them. When taxol is added to cells, it causes much of the free tubulin to assemble into microtubules. In contrast, colchicine prevents microtubule formation. Taxol is just as disruptive to dividing cells as colchicine, and both are used as anticancer drugs. Based on your knowledge of microtuble dynamics, suggest why both drugs are toxic to dividing cells despite their opposite actions.

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