The first stage of cell division Mitosis The first stage of cell division

4 Stages of Mitosis Mitosis, the process by which the duplicated contents of a cell’s nucleus divides into 4 equal parts, happens in 4 stages: 1) Prophase 2) Metaphase 3) Anaphase 4) Telophase

Prophase The phase of mitosis in which sister chromatids condense and the chromosomes become visible. Replicated chromosomes coil until they are finally condensed Visible under a microscope Membrane around the nucleus begins to break down, and nucleolus disappears Centrosomes head towards opposite ends of the cell Extending from the centrosomes, thread-like tubules begin to form spindle fibers As prophase progresses, spindle fibers extend away from centrosomes towards the centromeres on each chromosome

Metaphase The phase of mitosis in which the chromosomes are aligned across the center of the cell. Longest phase in mitosis Centrosomes reach opposite ends of the cell Chromosomes move towards the middle of the cell, eventually all lining up along the center Spindle fibers now stretch from the centrosomes to the centromere Each centromere becomes attached to two spindle fibers, one from each end of the cell

AnaPhase The phase of mitosis in which the centromere splits apart and the chromatids are pulled to opposite sides of the cell by the spindle fibers. The shortest phase Proteins holding the chromatids together at the centromere break apart Spindle fibers, stretched like elastic bands between the chromosomes at the center of the cell and the centrosomes ate the opposite ends of the cell, begin to retract While retracting, pull a chromatid with them towards the end of the cell Once the chromatids seperate, each is now considered a chromosome

Telophase The phase in mitosis in which two daughter nuclei are formed. Spindle fibers begin to disappear Membranes begin to form around each new daughter nuclei, one at each end of the cell Within nuclei, nucleolus begins to appear Chromosomes become less coiled, and unwind Mitosis is now complete! Although it is mitosis happens in these 4 stages, the process is a continuous one; it does not “rest” between stages

Cell division Part II: cytokinesis As already discussed, mitosis is simply the duplication and division of a cells nuclei. The process by which the entire actually divides is called cytokinesis. Specialized proteins around the middle of the cell starts to contract Contraction “pinches’ the cell membrane until the parent cell divides into 2 parts Each daughter cell has its own chromosomes and organelles now

Cytokinesis: Plant cells Although similar to the process animal cells, cytokinesis in plant cells is slightly different. This is because of the rigid cell wall. Golgi body starts to produce small vesicles Each carries sacs of materials to form new cell wall Vesicles line up between two nuclei forming a cell plate Cell plate grows and joins the old cell wall New cell walls are secreted on each side of the cell plate, dividing the cytoplasm in two Cell membranes form inside new cell wall, and division is complete