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Biology Classwork The Cell Cycle & Mitosis name ______________________ per __ date _____ The Cell Cycle Cell division is just one of several stages that a cell goes through during its lifetime. The cell cycle is a repeating series of events, including growth, DNA synthesis, and cell division. The cell cycle in prokaryotes is quite simple: the cell grows, its DNA replicates, and the cell divides. In eukaryotes, the cell cycle is more complicated. Eukaryotic Cell Cycle The diagram at left represents the cell cycle of a eukaryotic cell. As you can see, the eukaryotic cell cycle has several phases. The mitosis phase (M) actually includes both mitosis and cytokinesis. This is when the nucleus and then the cytoplasm divide. After the M phase, two cells result. The other three phases (G1, S, and G2) are generally grouped together as interphase. During interphase, the cell grows, performs routine life processes, and prepares to divide. These phases are discussed below. Interphase Interphase of the eukaryotic cell cycle can be subdivided into the following three phases, which are represented in the figure above: • Growth Phase 1 (G1): During this phase, the cell grows rapidly, while performing routine metabolic processes. It also makes proteins needed for DNA replication and copies some of its organelles in preparation for cell division. A cell typically spends Image courtesy of CK-12 Foundation and under the Creative Commons license CC-BY-NC-SA 3.0. most of its life in this phase. • Synthesis Phase (S): During this phase, the cell’s DNA is copied in the process of DNA replication. • Growth Phase 2 (G2): During this phase, the cell makes final preparations to divide. For example, it makes additional proteins and organelles. Mitosis Mitosis is a continuous process that results in two identical daughter cells (copies). Based on the events happening mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase. Prophase is the first phase of mitosis. Prophase begins with the shortening and tight coiling of DNA in chromatin form into rod-shaped chromosomes that can be seen with a light microscope. During the synthesis phase of the cell cycle, each chromosome is copied. The two copies of each chromosome—called chromatids—stay connected to one another by the centromere. At this time, the nucleolus and the nuclear membrane break down and disappear. Spindle fibers begin assembly, radiating from opposite poles of the cell in preparation for mitosis. Metaphase is the second phase of mitosis. During metaphase, kinetochore fibers move the chromosomes to the center of the dividing cell. During anaphase, the chromatids of each chromosome separate at the centromere and slowly move toward opposite poles of the dividing cell. After the chromatids separate, they are considered to be individual chromosomes. Telophase is the fourth phase of mitosis. After the chromosomes reach opposite ends of the cell, the spindle fibers disassemble and the chromosomes return to a less tightly coiled chromatin state. A nuclear envelope forms around each set of chromosomes, and a nucleolus forms in each of the newly forming cells. Cytokinesis, when the nucleus and then the cytoplasm divide, follows telophase. Two genetically identical cells is the result. Definitions _____ 1. division of the nucleus _____ 2. region of the chromosome where sister chromatids are attached _____ 3. division of the cytoplasm _____ 4. phase of mitosis in which spindle fibers attach to the centromere of each pair of sister chromatids _____ 5. coiled structures made of DNA and proteins _____ 6. phase of mitosis in which sister chromatids separate and the centromeres divide _____ 8. two copies of replicated DNA that make a chromosome _____ 9. the first and longest phase of mitosis _____ 10. uncoiled DNA _____ 11. a pair of the same chromosome _____ 12. phase of mitosis in which the chromosomes begin to uncoil and form chromatin Terms a. anaphase b. centromere c. chromatid d. chromatin e. chromosome f. cytokinesis h. homologous chromosomes i. metaphase j. mitosis k. prophase l. telophase Check your understanding: Comprehension Questions 1. What is the cell cycle? 2. What are the phases of the eukaryotic cell cycle? 3. In which phase does a cell spend most of its life? What happens during this phase? 4. What is cancer? What may cause cancer to occur? 5. What is the S phase? What happens during this phase? NOW PUT IT IN YOUR OWN WORDS. Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences. Your response should be 5 – 8 sentences long. 6. Describe the eukaryotic cell cycle, listing and discussing the main events of each phase.