18 Pogil Cell Cycle Regulation

Cell Cycle Regulation How does a cell know it is time to divide? Why? _________________________________________________________________________________o Quality control inspectors typically do not limit their product testing to the final product at the end ofo the assembly line. They monitor all aspects of production in hopes of preventing larger problems downo the line. Likewise, when cells are progressing through the cell cycle there are processes in place thato check on the cell’s progress. Is everything happening according to plan? Are there sufficiento resources to complete the task of cell division? Tightly regulating the cell cycle keeps a multicellularo organism healthy by conserving materials. This ensures that new cells receive accurate genetico information, and also prevents uncontrolled growth that may lead to diseases like cancer.o _________________________________________________________________________________ Model 1 - The Cell Cycle 1. Review the phases of the cell cycle in Model 1 by placing the abbreviated phase name (G1, S, G2 or M) next to the proper description. g1 The cell grows by producing more proteins and organelles. s DNA replication occurs. g2 The cell prepares for cell division with the appearance of centrosomes. m Mitosis and cytokinesis occurs. 2. Some cells, like mature nerve cells or muscle cells, do not divide. Other 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? g0 3. There are three regulatory checkpoints built into the cell cycle. a. Name the three checkpoints as shown on Model 1. G1 and g2 checkpoint , M checkpoint b. Indicate the phase of the cell cycle, and what part of the phase (early or later), where each checkpoint occurs. G1,g2,m-later 4. 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. g2 The DNA has been completely replicated and checked for errors. g1,g2 There is ample supply of energy and raw materials available. m All chromosomes are attached to the spindles. g1 There is adequate room in the environment for more cells. 5. Which checkpoint appears to regulate whether the cell is in G0 or not? g1 6. Predict the result of a mutation that allows a cell to move past checkpoint G1 even though the cell has not grown sufficiently. It may not form properly. It could be too small to survive. 7. Predict the result of a mutation that allows a cell to move past checkpoint G2 even though DNA replication has not been completed. The cell won't have the right DNA 8. Predict the result of a mutation that allows a cell to move past checkpoint M even though the chromosomes were not prepared for division. The cell won’t function like it’s supposed to. Read This! _________________________________________________________________________________ What determines if a cell is in G0 or going through the cell cycle? What determines a “pass” at a checkpoint during the cell cycle? These questions are answered by both intracellular and extracellular chemical signals. Growth factors are one type of chemical signal. These proteins are released by specialized cells and trigger cell division. Surface proteins tell cells to stop dividing if the environment gets too crowded and cells are touching with too much pressure. Enzymes called kinases provide the energy (through phosphorylation) for many of the processes that must happen for successful mitosis to occur. _________________________________________________________________________________ Model 2 - Cyclin and Kinase A B C 9. Identify the shape that represents the kinase in Model 2. A rectangle with a sharp dip 10. Identify the shape that represents cyclin in Model 2. A rectangle with a sharp side to fit something inside it 11. Recall that the purpose of the kinases is to phosphorylate other molecules, thus bringing them to a higher energy state. With this in mind, identify the three parts of the maturation promoting factor (MPF) shown in Model 2. The MPF is made of kinases,cyclin, and phosphate group 12. 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? g1,s,g2 13. 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. It stays the same. b. Describe the changes in the concentration of cyclin as the cell moves through different phases of the cell cycle. The concentration of cyclin doesn’t change throughout the cell cycle 14. 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 cyclin increases there is more bind to cdk so the concentration of mpf increases 15. 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, the cells would divide so there would be fewer cyclin molecules. 16. Considering both Model 1 and Model 2, which checkpoint in the cell cycle is regulated by the concentration of MPF? Justify your reasoning. G2 the mpf concentration is higher 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? Cells would not progress through even if they aren't ready 18. How might a cell be affected by the development of a degradation-resistant cyclin mutant? Explain. The cyclin would not be degraded and the mpf would always be active . 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 that regulate apoptosis (pre-programmed cell 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? g2 b. check for adequate room for more cells? g1 20. Create an analogy for the function of proto-oncogenes and tumor suppressor genes by assigning the role of a 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 Regulate cell cycle Tumor Suppressor Genes brake Slow down if too crowded