Mitosis

Purpose To grow more cells –Example: Growing taller, growing roots To reproduce asexually –Example: Hydra buds to reproduce Repair damaged tissue –Example: A tear in skin –cells multiply to repair the tissue.

Overview Cells divide into 2 daughter cells Daughter cells are identical to parent cells Done in somatic cells- typical body cells There are 4 stages of mitosis: –Prophase –Metaphase –Anaphase –Telophase/Cytokenesis The rest of the cell’s life is spent in interphase- the cell cycle.

Why study mitosis? Mitosis is a complicated process that is done flawlessly thousands of times per day. When mistakes occur, the result can be dangerous. Helps us to understand genetics and biotechnology.

Stage #1- Prophase Chromatin in the nucleus coils and become distinct chromosomes Chromosomes that were duplicated during the “S” phase join with their sister chromatid.— Join at the centromere A mitotic spindle grows out from centrosomes in the cytoplasm. The nuclear envelope disappears. Spindle attaches to the centromere (kineticore) and pulls the chromosomes to the center.

Stage #2-Metaphase Centrosomes are positioned at the poles. The chromosomes are lined up in the middle-the metaphase plate. The sister chromatids are lined up on either side of the plate. The spindle is attached to each chromatid and prepares for separation.

Stage #3-Anaphase The spindle fibers “reel” in the chromatids. The poles move farther apart. The microtubules which make up the spindle get shorter, pulling the chromatids toward the poles.

Stage #4-Telophase A nucleus begins to reform in the new cell. Chromosomes lengthen into chromatin. Mitotic spindle disappears. A cleavage furrow appears, separating the two cells. Cytokenesis pinches the cell into two separate cells.

Differences in mitosis Plant cells use telophase differently- they form a plate between the two new cells that becomes a cell wall.

Factors for mitosis Cells only divide when they are attached or anchored—anchorage dependence. Cells divide until they begin to touch one another-density-dependent inhibition These conditions prevent cells from dividing in the wrong environment or uncontrollably. --This is regulated by the cell cycle.