Mitosis Slides PDF

Cell Division  Genes and Proteins *Proteins do the work of the cell: growth, maintenance, response to the environment, reproduction, etc. Proteins are chains of amino acids. Each gene codes for a different protein. *All cells within an organism have the same genes. What makes cells d...

Cell Division  Genes and Proteins *Proteins do the work of the cell: growth, maintenance, response to the environment, reproduction, etc. Proteins are chains of amino acids. Each gene codes for a different protein. *All cells within an organism have the same genes. What makes cells different from each other is that different genes are turned on and turned off in different cells. Chromosomes The essential part of a chromosome is a single very long strand of DNA. This DNA contains all the genetic information for creating and running the organism.  Cell Cycle (interphase(G1,S,G2) Mitosis: prophase, metaphase, telophase and cytokinesis) Some cells divide constantly: cells in the embryo, skin cells, gut lining cells, etc. Other cells divide rarely or never: only to replace themselves. Actively dividing cells go through a cycle of events that results in mitosis. Most of the cycle is called “interphase” (G1,S,G2) During interphase the cell increases in size, but the chromosomes are invisible. *This is when the genetic material is doubled, and at any point when the cell is damaged, it will stop and repair or destroy itself! Mitosis (Prophase,metaphase,anaphase, telophase, & cytokinesis) Mitosis is normal cell division, which goes on throughout life in all parts of the body. *Mitosis occurs in eukaryotes. This is an sexual process. 1 parent turns into 2 daughter cells that are all identical Stages: Prophase,Metaphase, Anaphase, Telophase  Prophase In prophase, the cell begins the process of division. 1. The chromosomes condense. The proteins attached to the DNA cause the chromosomes to go from long thin structures to short fat one, which makes them easier to pull apart. 2. The double membrane that surrounds the nucleus dissolves, freeing the chromosomes to use the whole cell for division 3. The centrosomes move to opposite poles. During interphase, the pair of centrosomes were together just outside the nucleus. In prophase they separate and move to opposite ends of the cell. 4. The spindle starts to form, growing out of the centrosomes towards the chromosomes. Metaphase Metaphase is a short period where the chromosomes are lined up on the equator of the cell, with the centrosomes at opposite ends(poles) and the spindle fibers attached to the centromeres. Everything is aligned for the rest of the division process to occur.  Anaphase In anaphase, the centromeres divide. The spindle fibers contract, and the chromosomes are pulled apart (half of the chromosome is a chromatid) are pulled to opposite poles, towards the centrosomes. Telophase In telophase the cell actually divides. The chromosomes are at the poles The spindles disintegrate The nuclear membrane re-forms around the two sets of chromosomes. The cytoplasm is divided into 2 separate cells, the process of cytokinesis. Cytokinesis The organelles (other than the chromosomes) get divided up into the 2 daughter cells Plant and animal cells divide the cytoplasm in different ways. In plant cells, a cell plate is formed to separate the two new cells. It breaks in half & now you have two cells In animal cells, the membrane pinches between the two cells until they separate Summary of Mitosis Prophase: Chromosomes condense Nuclear membrane disappears centrosomes move to opposite sides of the cell Spindle forms Metaphase Chromosomes lined up on equator of spindle centrosomes at opposite ends of cell Anaphase Centromeres divide: each 2-chromatid chromosome becomes two 1-chromatid chromosomes Chromosomes pulled to opposite poles by the spindle Telophase Chromosomes de-condense Nuclear membrane reappears Cytokinesis: the cytoplasm is divided into 2 cells Cancer Cancer is immortal. It is a disease of uncontrolled cell division. It starts with a single cell that loses its control mechanisms due to a genetic mutation. That cell starts dividing without limit, and eventually kills the host. Normal cells are mortal. This means that they can divide about 30 times and then they lose the ability to divide, and eventually die(cell suicide). This “clock” gets re-set. Cancer cells escape this process of mortality: they are immortal and can divide endlessly. *Normal cells that suffer significant chromosome damage destroy themselves Cancer cells ignore the message and fail to kill themselves.* Cancer Progression Once a single cell starts growing uncontrollably, it forms a tumour, a small mass of cells. No further progress can occur unless the cancerous mass gets its own blood supply. A tumor with a blood supply will grow into a large mass. Eventually some of the cancer cells will break loose and move through the blood supply to other parts of the body, where they start to multiply. This process is called metastasis. *  Two basic treatments: surgery to remove the tumor, and radiation or chemicals to kill actively dividing cells. Sources of cancer: genetic, exposure to carcinogens (tobacco, asbestos, too much UV radiation etc.) and sometimes by chance, and genetics (we don’t fully understand)*