5. The mitotic cell cycle
A section of Biology, 9700
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The mitotic cell cycle in dividing cells is very carefully controlled. Complete Table 6.1 to show the correct order of stages in the mitotic cell cycle. Some of the stages have been completed for you. Table 6.1 stage of cell cycle G1 phase mitosis telophase cytokinesis At various points during the mitotic cell cycle, checks are made. A cell goes through cell death if errors occur that cannot be repaired. This makes sure that the daughter cells produced are genetically identical to each other and to the original cell. Drugs have been developed that can inhibit the mitotic cell cycle and cause the cell to carry out apoptosis. These drugs are used in the treatment of cancer. Vincristine and 5-fluorouracil are chemical compounds that act as cell cycle inhibitors and can lead to apoptosis. • Vincristine binds to spindle microtubules and prevents the spindle from carrying out its function. • 5-fluorouracil prevents the synthesis of thymine nucleotides. Complete Table 6.2 to show which event in the cell cycle will occur when Vincristine or 5-fluorouracil are added to healthy dividing cells at the start of the interphase stage of the cell cycle. Place a tick (3) if the event will occur or a cross (7) if the event will not occur. All boxes in the table should be completed. Table 6.2 event in cell cycle compound S-phase completes cell enters prophase of mitosis chromosomes line up at spindle equator sister chromatids move towards opposite poles Vincristine 5-fluorouracil Vincristine has been used in the treatment of certain types of leukaemia. is a photomicrograph of a blood smear of a person with one form of leukaemia, which affects lymphocytes. red blood cell Describe how: • the blood smear shown in differs from a blood smear of a healthy person • the lymphocytes in a person with leukaemia, such as those shown in , differ from those of a healthy person. blood smear differences lymphocyte differences
9700_s20_qp_22
THEORY
2020
Paper 2, Variant 2
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Blood cells are formed from tissue stem cells in the bone marrow. These bone marrow stem cells go through a number of mitotic cell cycles to form the fully functioning blood cell. shows the three main stages of the cell cycle. interphase mitosis cytokinesis The activity of genes changes during the mitotic cell cycle. When genes are being expressed, the cell produces many messenger RNA (mRNA) molecules and ATP molecules. Explain what is meant by a gene. Name the main stage of the cell cycle in during which most mRNA and ATP is formed. is an incomplete diagram of an ATP molecule. phosphate sugar base On : • complete the diagram of the ATP molecule • write the name of the base in the space provided • write the name of the sugar in the space provided. The base shown in has a double ring structure. State the term for a base that has a double ring structure. Suggest and explain the role of mitosis in the formation of blood cells by the bone marrow stem cells.
9700_s20_qp_23
THEORY
2020
Paper 2, Variant 3
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A single skin cell was isolated and transferred to growth medium in a sterile Petri dish. The Petri dish was incubated for 16 days. During this time, the number of skin cells multiplied as a result of repeated mitotic divisions. One of the chromosomes in the nucleus of each skin cell has a telomere that contains many repeats of the base sequence TTAGGG. On each of days 4, 8, 12 and 16 of the incubation period, a single cell was removed from the Petri dish. The total number of bases in the telomere of this chromosome was determined for each cell. Each of the four cells had a different total number of telomere bases for this chromosome: 5548, 5580, 5645 and 5700. What was the total number of telomere bases in the chromosome from the cell that had undergone the most mitotic divisions?
9700_s21_qp_12
MCQ
2021
Paper 1, Variant 2
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Questions Discovered
324