cell cycle regulation, Exercises of Biology

Download cell cycle regulation and more Exercises Biology in PDF only on Docsity!

Bo BE ad) a) Do ny) BB) Cell Cycle Regulation How daes a cell know it is time to divide? Why? . Quality control inspectors typically do not limit their product testing to the final product at the end of the assembly tine. They monitor all aspects of production in hopes of preventing larger problems down the line. Likewise, when cells are progressing through the cell cycle there are processes in place that check on the cell’s progress. Is everything happening according to plan? Are there sufficient resources to com- plete the task of cell division? Tightly regulating the cel] cycle keeps a multicellular organism healthy by conserving materials. This ensures that new cells receive accurate genetic information, and also prevents uncontrolled growth that may lead to diseases like cancer. Model 1 — The Cell Cycle G, Checkpoint 1. Review the phases of the cell cycle in Model 1 by placing the abbreviated phase name (G,, 8, G, or M) next to the proper description. G, fi The cell grows by producing more proteins and organelles. $ DNA replication occurs. & ‘The cell prepares for cell division with the appearance of centrosomes. iM : Mitosis and cytokinesis occurs. 2. Some cells, like mature nerve cells or muscle cells, do not divide. Orher cells will divide only when the cellular environment signals that it is necessary. According to Model 1, what “phase” of the cell cycle are these cells said to be in when they are not dividing or planning to divide? When cells are not dividing or planning to divide, they go inta a “phase” called G, Cell Cycle Regulation an 161 Bs 162 . There are three regulatory checkpoints buile into the cell cycle. a. Name the three checkpoints as shown on Model 1. G, checkpoint, G, checkpoint, and M checkpoint. . & Indicate the phase of the cell cycle, and what part of the phase (early ot later), where each checkpoint occurs. . The G, checkpoint occurs in the later part of G., The G, checkpoint occurs in the later part of G, The M checkpoint occurs in the later part of Mitosis, Progression through the cell cycle is dependent on both extra- and intracellular conditions. Consider the following conditions. Indicate which checkpoint(s) most likely responds to that condition. a. The DNA has been completely replicated and checked for errors. G, checkpoint. b, There is ample supply of energy and raw materials available. G, and G, checkpoints. ¢, Alf chromosomes are attached to the spindles. M checkpoint. d. There is adequate room in the environment for more cells. G, checkpoint. . Which checkpoint appears to regulate whether the cell is in G, or nov? The G, checkpoint is the point in the cycle where the cell goes into or out of G, |. Predict the result of a mutation that allows a cell to move past checkpoint G, even though the cell has nat grown sufficiently. The daughter cells would be small and possibly not able to store enough nuirients within the cell to survive. . Predict the result of a mutation that allows a cell to move past checkpoint G, even though DNA replication has not been completed. The DNA in the daughter cells would not be complete and the cells would not survive, . Predict the result of 2 mutation that allows a cell to move past checkpoint M even though the chromosomes were not prepared for division. The chromosomes might end up in the wrong daughter cell. For example, one cell might get bath copies of a chramosome while the other gets none. POGIL™ Activities for AP* Biology ~an.a.aneaeaanmaanmannannagnaaaanaanaaanaenenaaseae na ll. 12. Ba. 14. 15. 16. om Recall that the purpose of the kinases is to phosphorylate other molecules, thus bringing them toa higher energy state. With this in mind, identify the thtee parts of the maturation promoting factor (MPF) shown in Model 2. : The MPF is made from a kinase (Cdk), a cyclin, and a phosphate group (P), The graph in Model 2 divides the cell cycle into “interphase” and “mitosis.” Which of the phases of the cell cycle in Model 1 fall into the “interphase” time frame? G, S, and G, ave part of interphase. Consider the graph in Model 2. a, Describe the changes in the concentration of cyclin dependent kinase (Cdk) as the cell moves through different phases of the cell cycle. The concentration of Cdk does not vary throughout the cell cycle. 6, Describe the changes in the concentration of cyclin as the cell maves through different phases of the cell cycle. The concentration of cyclin is minimal at the start of G,, but steadily increases until partially through mitosis, and then quickly drops to a minimal level once again. Propose an explanation for the change in the maturation promoting factor (MPF) concentration throughout the cell cycle based on your knowledge of the concentrations of Cdk and cyclin. As the concentration of cyclin increases, there is more cyclin to bind to the Cdk, so the concentration of MPF increases. Can the change in cyclin concentration during mitosis be explained by the fact that the cell divides in two.and thus divides the material in the cell into two smaller volumes? If no, propose an explanation for the change in concentration that is seen. No. When the cell divides there would be fewer cyclin malecules in each daughter cell than in the parent cell, but the daughter cells have a smaller volume, so the concentration should be the same. The graph indicates that the cyclin concentration approaches zero after mitosis, so the molecule must be ‘used up ina reaction or decomposed after mitosis. Considering both Model 1 and Model 2, which checkpoint in the cell cycle is regulated by the concentration of MPF? Justify your reasoning, The G, checkpoint because the MPF concentration is highest just before the cell goes into M phase. POGIL™ Activities for AP* Biology _— mmm mmm se ee ee ee eee ee ee ee ee we ee wee ee ee Read This! After MPF has done its job of phosphorylation, the cyclin portion of the complex is degraded. This means that the protein is broken up into parts that can be recycled by the cell. The kinase is not degraded, but instead used again as the cell goes through another cycle of division. 17. If cyclin was always available in the cell at high concentrations, what effect would this have on the cell cycle? Calls would progress through mitosis even if they were not ready. 18. How might a cell be affected by the development of a degradation-resistant cyclin mutant? Explain. [the cyclin could not be degraded, the MPF would always be active. Therefore, the cell would be continuously pressured to mave through the G, checkpoint, even if the conditions were not right. Read This! Cyclin proteins are encoded by a group of genes called proto-oncogenes. Besides cyclins, which function inside the cell, other proteins made by genes from this group are embedded in the cell membrane and receive extracellular signals that help to regulate the cell cycle and slow down the differentiation of new cells. Tumor suppressor genes make up another group of genes that regulate cell division. Genes from this group produce proteins that signal cells when they are getting too crowded, proteins whose function is to repair DNA, and still other proteins chat regulate apoptosis (pre-programmed cel! death). A tumor suppressor gene called p53 causes apoptosis when the cell is worn out or when defects are detected, 19. At which checkpoint in the cell cycle would a tumor suppressor gene a. repair DNA function? G. ‘2 6. check for adequate room for more cells? G i 20. Create an analogy for the function of proto-oncogenes and tumor suppressor genes by assigning the role ofa car's accelerator and brake pedals to'each group. Using your previous knowledge, the information given above, and information in Model 2, complete the table below. Regulatory Genes Pedal Justification Proto-oncogenes Accelerator (gas) | Cyclin allows cells to pass through G, and divide. Would tend to slow down division when cells are Brake crowded (suppressor means to slow down or stop something from happening). Tumor suppressor genes Cell Cycle Regulation ’ 165