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Noelle Jessup AP Biology 1. b) S Interphase is the first step in the cell cycle, when the cell is preparing to divide by synthesizing proteins and replicating DNA. The chromosomes must be replicated in the S phase of interphase so that in the next phase, G2, the cell can prepare to divide, while still retaining the identical DNA. 2. a) G2, because if the checkpoint isn’t working properly the cells can undergo rapid/unregulated division G2 is considered the most important part of the cell cycle, because any potential problem caused at the end of this checkpoint could lead to cancer. The checkpoint ensures that all of the cells are undamaged so that they can move onto mitosis. It looks for any damaged cells that may have been a result of replication and also checks for the proteins needed for cellular division. As for the other answers; the mitotic spindle isn’t formed until prophase of mitosis and is not responsible for the daughter cells containing proper machinery. Interphase is not a result of sexual reproduction, and interference here would not cause instant cell death. The S phase does not include binary fission, in fact, none of the phases in eukaryotic cells do. 3. a) Doubles it The S phase doubles the amount of DNA to 92 chromatids; 46 chromosomes with 2 chromatids each. The cell continues to hold the chromatid number at 92 until the conclusion of mitosis. 4. b) Cyclin-Dependent Kinases Also called CDK’s; which partner with a family of proteins called cyclins. It is activated when it is bound to cyclin and interacts with various other proteins that allow the cell to move from G2 into Mitosis. 5. d) G2; prevents the cell from moving onto mitosis If there is damage in any of the cells before they undergo mitosis and it is not fixed, when the cells are replicated in the process of mitosis, they too will be damaged. To prevent this they must go through the G2 checkpoint. 6. c) To allow the microtubules to attach to the chromatids The kinetochores are formed in prometaphase, and serve the purpose of preparing the chromosomes for metaphase. In metaphase the chromatids will have to be lined up on the metaphase plate. Noelle Jessup AP Biology 7. d) cytokinesis The cleavage furrow is the start of the cell physically splitting. This occurs during telophase and is also known as cytokinesis. The cleavage furrow itself is formed by tightening a “ring” around the cell until it is pinched into two separate parts called daughter cells. 8. c) prophase, metaphase, anaphase, telophase Prophase is the first and longest phase, where the chromosomes become visable and the centrioles separate and move to opposite poles. Metaphase is the second, where the chromosomes line up across the center of the cell and become connected to the spindle fiber. Anaphase is the third, where the sister chromatids separate into individual chromosomes and are pulled apart. The fourth and last phase is telophase, when the chromosomes gather at opposite cell ends and lose the “rod-like” shape. Two new membranes are then formed around each section of DNA and spindle fibers disappear. 9. c) Both A and B Reductional division is a process where only half of the number of chromosomes in the cells undergo meiosis, as compared to the parent cells. This means that the cells that result from meiosis are haploid, and carry only half of the normal DNA that is present in the somatic cells. 10. b) Separation of homologous chromosomes In meiosis I the cell separates the homologous chromosomes, whereas in meiosis II the cell separates the sister chromatids.
