Biol What is Mitosis Notes

Mitosis What is (and is not) mitosis? Mitosis is nuclear division plus cytokinesis, and produces two identical daughter cells during prophase, prometaphase, metaphase, anaphase, and telophase. Interphase is often included in discussions of mitosis, but interphase is technically not part of mitosis, but rather encompasses stages G1, S, and G2 of the cell cycle. Interphase The cell is engaged in metabolic activity and performing its prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of which are organizational sites for microtubules. Prophase Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle. Prometaphase The nuclear membrane dissolves, marking the beginning of prometaphase. Proteins attach to the centromeres creating the kinetochores. Microtubules attach at the kinetochores and the chromosomes begin moving. Metaphase Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome. Anaphase The paired chromosomes separate at the kinetochores and move to opposite sides of the cell. Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules. Telophase Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage. Cytokinesis In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus. In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells. Mitosis Notes Cell division occurs in a series of stages, or phases. 1st: INTERPHASE • Chromosomes are copied (# doubles) • Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy (sister chromosome) change to sister chromatids at Sister chromatids end of this phase Centromere 2nd: PROPHASE • Mitosis begins (cell begins to divide) • Centrioles (or poles) appear and begin to move to opposite ends of cell • Spindle fibers form between the poles 3rd: METAPHASE • Chromatids (or pairs of chromosomes) attach to the spindle fibers Sister chromatids 4th: ANAPHASE • Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell Sister chromatids split 5th: TELOPHASE • Two new nuclei form • Chromosomes appear as chromatin (threads rather than rods) • Mitosis ends 6th: CYTOKINESIS • Cell membrane moves inward to create two daughter cells - each with its own nucleus with identical chromosomes Mitosis Notes Name ______________________ __________ _________________ occurs in a series of stages, or _____________. 1st: _______________ • Chromosomes are ___________ (# doubles) • Chromosomes appear as threadlike coils (__________________) at the start, but each chromosome and its copy (____________ chromosome) change to sister chromatids at Sister chromatids end of this phase _________________ 2nd: ______________ • ______________ begins (cell begins to divide) • __________________ (or poles) appear and begin to move to opposite ends of cell • ____________ _________ form between the poles 3rd: _______________ • _________________ (or pairs of chromosomes) attach to the spindle fibers Sister chromatids 4th: _______________ • Chromatids (or pairs of chromosomes) _______________ and begin to move to ________________ ends of the cell Sister chromatids split 5th: _______________ • Two new _____________ form • Chromosomes appear as chromatin (_____________ rather than __________) • ________________ ends 6th: _______________ • Cell membrane moves inward to create two _________________ cells - each with its own ________________ with identical _____________________