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Cytoskeleton: Mitosis and Meiosis

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A. Drugs that inhibit microtubule assembly are administered for some medical conditions. What will occur to the cell as a result? For what type of conditions would such a drug be given?

B. Colchicine is a chemical used to treat dividing plant cells to ensure that chromosomes of cells undergoing mitosis will be visible. How does colchicine achieve this effect? What is the natural source of colchicines.

C. Many conditions genetically predispose individuals to develop cancer, but these individuals contain no unusual chromosome(s). Does the lack of a visible chromosome defect make it unlikely that cancers in these individuals are caused by changes in the DNA? Explain your answer

D. How are binary fission and mitosis different? How are they similar?

E. Why do some cells of the human body (for example epithelial cells) continue to divide, yet other cells (e.g., neurons) lose their ability to replicate once they are mature? Describe some of the latest research efforts to induce cell division in nerve cells.

F. About 40 years ago, some researchers reported that they could transfer learning from one animal (Planaria, a type of flatworm) to another by feeding trained animals to untrained animals. Further, they claimed that RNA was the active molecule of learning. Given your knowledge of the roles of RNA and protein in cells, do you think that a specific memory (for example, remembering the base sequences of codons of the genetic code) could be encoded by a specific molecule of RNA and that this RNA could transfer that memory to another person? In other words, someday, could you learn biology by popping an RNA pill? If you could, how would the pill work? If you think the RNA pill wouldn't work, can you propose a reasonable hypothesis for the Planaria results? How would you test your hypothesis?

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A. Microtubules can be inhibited in polymerization or de polymerization by dilantin, vinca alkaloids (vinblastine, vincristine, and vinorelbine), colchicine, colcemid, taxanes (taxol and taxotere), epothilones and nocadazol. For a detailed list of microtubule function affecting chemicals see http://parasitology.informatik.uni-wuerzburg.de/login/n/h/2322.html

Microtubules have may functions in the cell including cell division, signaling, and intracellular trafficking. These inhibitors have been used as anti-cancer and antiparasitic treatments formerly to treat gout and also to treat pericarditis. Cells that divide rapidly are more susceptible to the effects of microtubule affecting drugs and their net result is an inability of cells to divide.

Additional references:

B. Colchicines bind to soluble tubulin subunits and prevents their polymerization into microtubules. Additionally colchicine also binds to the positive cap of the growing end on microtubules that attaches to centromeres this leads to depolymerization from the negative end and serves as a label for chromosomes undergoing mitosis. A natural source of colchicines can be found in plants of the genus Colchicum (Autumn crocus, Colchicum autumnale, also known as the "Meadow saffron"). ...

Solution Summary

Answers with web references to several questions involving the cytoskeleton.

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Molecular Biology of the Cell

1. Compare and contrast, in depth, the cellular processes of mitosis and meiosis. Include interphase in your explanation. Chromosomal movement and status must be included in your answer. You may include a diagram to explain your answer but you must discuss each portion of the diagram.

2. Explain the following signaling pathways in a cell: endocrine signal, paracrine signal, autocrine signaling and give specific examples of each.

3. If you lay out end-to-end all 46 chromosomes found in the human genome the length would total about 3 meters (~10 feet). Please explain fully how that much DNA fit into a eukaryotic nucleus that is usually less than 20µm in diameter.

4. The endosymbiotic theory postulates that the mitochondria and chloroplasts were once free-living organisms. Please explain this theory and give at least one specific example for each organelle that would support the theory that they were once free-living. In addition, some scientists argue that flagellum and cilia were once free living organisms. Please give an argument that either supports or rejects this argument.

5. Please discuss, in depth, the major components of the cytoskeleton. Please discuss how the cytoskeleton aids in the organization of the eukaryotic cell. Include in this answer the major functions of each.

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