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Mitosis Mitosis is the process by which new cells are generated. Mitosis produces 2 genetically identical daughter cells Overview of Mitosis: Parent cell Mitosis Replicated chromosomes condense at the start of mitosis Sister chromatids separate and two daughter cells are formed. Parent cell and daughter cell contain the same complement of chromosomes. The cell cycle: Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis. Figure 12.5x Mitosis How do spindle fibers move the chromosomes? The kinetochore is a specialized region on the centromere where spindle fibers attach Motor molecules of the kintochore walk along the microtubule, taking the chromosome with it As the chromosomes move toward the poles, the microtubules are broken down at the kinetochore end Motor molecules "walk" along a microtubule track Transport vesicle ATP Kinesin Microtubule ADP+Pi ATP ADP+Pi After the nucleus divides, cytokinesis divides the cytoplasm, forming two separate cells Figure 8.9a Cytokinesis in animals Cleavage furrow Mitosis in a plant cell Bacteria divide by binary fission Bacteria divide by binary fission Bacteria divide by binary fission Unregulated cell division can lead to cancer Many factors interact with each other to determine whether a cell will undergo mitosis Cell cycle checkpoints normally insure that DNA replication and mitosis occur only when conditions are favorable and the process is working correctly. Cell-Cycle Checkpoints G2 checkpoint Pass this checkpoint if: • cell size is adequate • chromosome replication is successfully completed M Mitosis G2 First gap Metaphase checkpoint G1 Pass this checkpoint if: • all chromosomes are attached to mitotic spindle G1 checkpoint S Pass this checkpoint if: • cell size is adequate • nutrient availability is sufficient • growth factors (signals from other cells) are present Cell cycle proteins regulate whether a cell will proceed past a particular cell cycle checkpoint cyclin - a protein whose amount varies cyclically cdk - another cell division control protein - a cyclin dependent kinase; active only when bound to cyclin MPF - mitotic promoting factor... • MPF is a kinase enzyme, ones that switches on/off target proteins by phosphorylating them..... • [cyclin + cdk = MPF]... favors Mitosis • leads to destruction of cyclin itself MPF levels rise, causing the cell to pass through the G2 checkpoint Growth factor proteins are signal molecules that trigger a signaltransduction pathway leading to cell division Platelet-derived growth factor Cell division is also dependent on environmental factors Unregulated cell division can lead to cancer Mutations in genes that encode cell cycle proteins can lead to unregulated growth, resulting in tumor formation and ultimately invasion of cancerous cells to other organs. Cancer cells have escaped cell cycle controls and divide excessively Figure 12-17x1 Breast cancer cell Figure 12-17x2 Mammogram: normal (left) and cancerous (right) CANCER SPREADS