Chapter 6 Section 2 THE CELL CYCLE Grade 10 Biology Fall 2010 Bell Ringer A typical eukaryotic cell spends 90% of its time in: 1. A. B. C. D. Mitosis Anaphase Interphase Cytokinesis 2. What do you think a cell spends its life cycle doing? Objectives Identify the major events that characterize each of the 5 phases of the cell cycle Describe how the cell cycle is controlled in eukaryotic cells Relate the role of the cell cycle to the onset of cancer The Life of a Eukaryotic Cell Cell division in eukaryotes is more complex than in prokaryotes Involves cytoplasm, chromosomes inside nucleus, and internal organelles The Cell Cycle Cell cycle: repeating sequence of cellular growth and division during the life of an organism A cell spends 90% of its time in the first three phases of the cycle Interphase Only enters the last two phases of cycle if it’s about to divide Cell Cycle The Cell Cycle Phase #1: First growth (G1) phase Cell grows rapidly and caries out routine functions Occupies major portion of cells life Cells that are not dividing remain in G1 phase Most muscles and nerve cells never divide If these cells die the body cannot replace them The Cell Cycle Phase #2: Synthesis (S) phase Cell’s DNA is copied At the end of the phase, each chromosomes consists of two chromatids attached at the centromere The Cell Cycle Phase #3: Second growth (G2) phase Preparations are made for the nucleus to divide Hollow protein fibers called microtubules are rearranged during G2 in preparation for mitosis The Cell Cycle Phase #4: Mitosis Mitosis: nucleus of a cell is divided into two nuclei Each nucleus ends up with the same number and kinds of chromosomes as the original cell The Cell Cycle Phase #5: Cytokinesis Cytkinesis: the process during cell division in which the cytoplasm divides Cell Cycle The Cell Cycle Mitosis and cytokinesis produce new cells that are identical to the original cells Allows organisms to grow, replace damaged tissues, and in some organisms reproduce asexually Control of the Cell Cycle How does a cell know when to divide? Cells have a system that controls the phases of the cell cycle Control of the Cell Cycle Cell cycle as key checkpoints at which feedback signals from the cell can trigger the next phase of he cell cycle Other feedbacks can delay the next phase Cell cycle in eukaryotes us controlled by many proteins Control of The Cell Cycle Three Checkpoints Checkpoint #1: Cell growth (G1) checkpoint Makes the decision of whether the cell will divide If conditions favorable and cell is healthy and large enough, certain proteins will stimulate cell to begin synthesis (S) phase S phase, cell copies DNA If conditions are not favorable, cells can stop at this checkpoint Cells can also stop at this check point if cell needs to go into resting period Nerve, muscle cells Control of the Cell Cycle Checkpoint #2: DNA synthesis (G2) checkpoint DNA replication is checked by DNA repair enzymes If checkpoint passed, proteins trigger mitosis Control of the Cell Cycle Checkpoint #3: Mitosis checkpoint Checkpoint triggers the exit of mitosis Signals the beginning of the G1 phase, the major growth period of the cell When Control is Lost Cancer If gene that controls the proteins that regulate cell growth and division is mutated, protein may not function and regulation of cell growth and division can be disrupted Cancer: the uncontrolled growth of cells, may result Disorder of cell division Cancer cells do not respond normally to body’s control mechanisms When Control is Lost Some mutations cause cancer Over producing growthpromoting molecules Inactivating the control proteins that normaly act to slow or stop the cell cycle Review Differentiate between the G1, G2, and S phases of the eukaryotic cell cycle 2. Relate what occurs at each of the three principal check points in the cell cycle 3. Why are individual chromosomes more difficult to se during interphase than during mitosis ? 4. In the cell cycle of typical cancer cells, mutations have caused: 1. A. B. C. Slower growth A failure in mitosis Uncontrolled growth Answers G1: growth and development; S: DNA is copied; G2: preparations made for nucleus to divide 2. Checkpoint 1: makes decision if cell will divide; Checkpoint 2: DNA replication is checked, triggers mitosis; Checkpoint 3: checkpoint triggers exit from mitosis 3. Individual chromosomes are more difficult o se during interphae than in during mitosis because they haven't condensed and divided 4. C) uncontrolled growth 1.