The Cell Cycle Mitosis Cytokinesis and Cancer Mitosis

The Cell Cycle: Mitosis, Cytokinesis and Cancer

Mitosis is. . . � 2 nd stage of the cell cycle (usually the shortest) �Results in 2 daughter nuclei ◦ Contain the same number/kinds of chromosomes

�Sister Chromatids: the DNA molecules that replicated during interphase join together to form chromosomes �Centromere: joins the sister chromatids

The Stages of Mitosis. . . 1. 2. 3. 4. 5. Early Prophase Late Prophase Metaphase Anaphase Telophase

1. Early Prophase Terms to know. . . �Spindle fibres: tiny tube like structures made of protein ◦ Controlled by centrioles �Centrioles: organelles that “organize” spindle fibres ◦ Move to opposite ends of the cell ◦ Not found in plant cells

�Chromosomes coil in “X” shapes and become visible under a light microscope �Nucleolus disappears and nuclear membrane breaks down �Spindle fibres form and stretch across cell

2. Late Prophase �Spindle fibres are completely formed �Chromosomes attach to spindle fibres at centromeres �Nuclear membrane completely disappears

3. Metaphase �Spindle fibres pull X-shape chromosomes into a straight line across the centre (equator) of the cell

4. Anaphase �Spindle fibres begin to shorten �Centromere is pulled apart, forcing sister chromatids to opposite ends of the cell �Separate sister chromatids now considered chromosomes

5. Telophase �Complete set of chromosomes at each end of cell �Spindle fibres begin to disappear �Nuclear membrane reforms around each set of chromosomes �Nucleolus appears in each nucleus Now that there are 2 nuclei in the cell, the cell can divide!

Cytokinesis is. . . �Final stage of the cell cycle �Separates the 2 nuclei into 2 daughter cells ◦ Daughter cells are identical to parent cells �Animal Cells: cell membrane pinches together to divide cell’s cytoplasm and organelles �Plant Cells: cell plate forms along entre of the cell to divide cell into 2 daughter cells

Checkpoints in the Cell Cycle �Checkpoints monitor the activities within a cell during the cycle �Special proteins send info to the nucleus, which decides if the cell is ready to divide �A cell will NOT divide if. . . ◦ There aren’t enough nutrients to support growth ◦ DNA has not been replicated ◦ DNA is damaged

The Cell Cycle and Cancer �Gene mutations could result in a faulty checkpoint protein ◦ RESULT: cell cycle control is lost! ◦ Ex. : cell could divide uncontrollably �Cancer: certain diseases that are caused by uncontrolled cell division

�Healthy/normal cells grow in a single layer and stop when told by neighbour cells �Cancer cells do NOT stop ◦ Form multiple layers tumours �Cancer cells have large, abnormal nuclei ◦ Checkpoints aren’t working, causing chromosomes to divide incorrectly

�Cancer cells attract blood vessels, which deliver nutrients �Cancer can spread if tumour cells break away and are carried by blood vessels to a new location �Cancer researchers are studying how the cancer cells mutate genes (producing non-functioning proteins) and how they can treat the disease