CELL
DIVISION,
MITOSIS,
MEIOSIS &
CANCER
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2020/2021
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CELL
DIVISION,
MITOSIS,
MEIOSIS &
CANCER
CELL DIVISION
(^) The Cell cycle , the ordered sequence of events that occur in a cell in preparation for cell division. (^) The cell cycle is a four- stage process in which the cell increases in size (gap 1, or G1, stage), copies its DNA (synthesis, or S, stage), prepares to divide (gap 2, or G2, stage), and divides ( mitosis, or M, stage). (^) The stages G1, S, and G make up interphase , which accounts for the span between cell divisions. (^) Mitosis is further divided into 4 phases
THE 5 PHASES OF MITOSIS
1. Interphase: (^) The stages in the cell cycle between one mitosis and the next, which includes G1, S and G2 , is known as interphase. (^) The DNA in the cell is copied in preparation for cell division, this results in two identical full sets of chromosomes. (^) Outside of the nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division. (^) During interphase, microtubules extend from these centrosomes. 2. Prophase: (^) The chromosomes condense into X-shaped structures that can be easily seen under a microscope. (^) Each chromosome is composed of two sister chromatids, containing identical genetic information. (^) The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on. (^) At the end of prophase the membrane around the nucleus in the cell dissolves away releasing the chromosomes. (^) The mitotic spindle, consisting of the microtubules and other proteins, extends across the cell between the centrioles as they move to opposite poles of the cell.
THE 5 PHASES OF MITOSIS
3. Metaphase: (^) The chromosomes line up neatly end-to-end along the center (equator) of the cell. (^) The centrioles are now at opposite poles of the cell with the mitotic spindle fibers extending from them. (^) The mitotic spindle fibers attach to each of the sister chromatids. 4. Anaphase: (^) The sister chromatids are then pulled apart by the mitotic spindle which pulls one chromatid to one pole and the other chromatid to the opposite pole. 5. Telophase: (^) At each pole of the cell a full set of chromosomes gather together. (^) A membrane forms around each set of chromosomes to create two new nuclei. (^) The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis.
MEIOSIS:
OVERVIEW
(^) Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. These cells are our sex cells ( gametes ) – sperm in males, eggs in females. (^) These four daughter cells only have half the number of chromosomes of the parent cell – they are haploid.