The drug Taxol, or Paclitaxel, is used to treat patients with a variety of cancers, including breast, lung and ovarian cancers. The drug works by stabilizing microtubules, and preventing their disassembly. The goal of the drug is to prevent dividing cells from being able to complete mitosis. As a result, cancerous cells can no longer divide. In a cell treated with Taxol, at what stage of mitosis will the cells arrest?

Question

A.  Prior to metaphase
B.  Anaphase
C.  Telophase
D.  Cytokinesis

Clarify Question
 · What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

  Gather Content
  · What do you know about movement of chromosomes in mitosis? How does it relate to the question?

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?

  Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

  Reflect on Process
  · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

A.  Prior to metaphase

Clarify Question
  · What is the key concept addressed by the question?
        o The question asks about the role of microtubules in moving chromosomes during mitosis.
· What type of thinking is required?
        o You are being asked to apply your understanding of how chromosomes move by the assembly and disassembly of microtubules to predict where taxol would arrest a cell in mitosis.
· What key words does the question contain and what do they mean?
        o Taxol stabilizes microtubules and prevents them from diassembling – microtubules grow by adding molecules of tubulin and shrink by disassembly, losing tubulin molecules.

  Gather Content
  · What do you know about movement of chromosomes in mitosis? How does it relate to the question?
        o Chromosomes move by being pushed and pulled by microtubules.  If more tubulin is added to a microtubule it will grow and push a chromosome that it is attached to.  If tubulin is removed from a microtubule by disassembly, then any attached chromosome will be pulled.

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?
        o In anaphase, telophase and cytokinesis the chromosomes are being pulled to either end of the cell.  This will require disassembly of the tubulin molecules attached to the chromosome.

  Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Even though the later stages do require microtubule disassembly, the movement of the chromosome to the equator of the cell also requires some pushing and pulling of the chromosome.  Thus if taxol is added it will affect this movement of the chromosome before the later stages and the cell will arrest before it gets to metaphase.

  Reflect on Process
  · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to apply your understanding of how chromosomes move during mitosis to predict the effects of taxol. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you recall that chromosomesneeded to be pushed and pulled by the assembly and disassembly of microtubules to get them to the equator in metaphase?  Did you think that pulling chromosomes only occurred in anaphase and later steps of mitosis?  Did you realize that pulling chromosomes requires the disassembly of microtubules?