M I T O S I S
Mitosis Mitosis is the type of cell division that occurs for growth (adding new cells) and repair (replacing old or damaged cells). It results in two daughter cells that have identical chromosomes to the parent cell. Almost every cell in the human body has an identical set of 46 chromosomes, produced through the process of mitosis.
Structure of eukaryotic chromosomes During most of a cell s life cycle, the DNA strands are so long and thin that they are not visible under a microscope. The loose DNA is called chromatin. Prior to cell division, the DNA coils several times around proteins (histones) to form shorter, thicker structures called chromosomes that are visible under a microscope.
Coiling of DNA http://www.youtube.com/watch?v=n5zfoscowqo
Cell Cycle Animation During G1: Normal cell activities. During S: Synthesis of new DNA Each chromosome is replicated, forming 2 identical copies of each. Interphase (between cell divisions): G1, S and G2. Chromosomes are not visible. During G2: Final preparations for cell division.
G1: cells grow, carry out their normal functions and replicate their organelles Synthesis: cells make a copy of nuclear DNA (at the end of this phase there are 2 sets of DNA). G2: cells continue to carry out normal functions and additional growth occurs
Chromosome/Centromere/Sister Chromatid The two identical copies of each chromosome produced in the S phase are attached together by centromeres. Each strand is called a sister chromatid.
http://www.youtube.com/watch?v=vgv3fv-uzyi
http://www.youtube.com/watch?v=c6hn3sa0ip0
Prophase: Phases of Mitosis Chromosomes condense and become visible. Nuclear membrane dissolves. Centrioles start to migrate to poles
Metaphase: Each chromosome (with 2 sister chromatids) line up along the middle of the equator. Spindle fibers attach to the centromere of each chromosome.
Anaphase: Centromeres separate (split apart) and sister chromatids (now each a chromosome) move to opposite poles.
Telophase/ Cytokinesis: New nuclei form, chromosomes unwind back to chromatin. Cell divides into two new cells. In plant cells, a cell plate forms between the two cells. In animal cells, a cleavage furrow forms as the parent cell is pinched into two cells.
Telophase/Cytokinesis: Telophose has to do with the nuclei forming around the two sets of chromosomes (which are uncoiling), at opposite poles of the cell. Cytokinesis is the process by which the cytoplasm divides to form two new cells.
Actively growing tissue, such as the tip of a plant root, will have cells undergoing mitosis. Identify as many stages as you can in the picture below.
Cancer Cancer is caused by uncontrolled cell growth in which cells don t respond to normal cell cycle controls, such as contact inhibition. - Benign growth: Harmless. - Malignant growth: Cancerous - Metastasis: Spread of cancer in the body
Why Cancer Kills Since cancer cells are always undergoing cell division (mitosis) they do not spend any time in interphase doing their normal functions. They deprive surrounding normal tissue of nutrients causing them to die. Eventually, there are not enough healthy, normal cells in the organ to allow it to function properly.
The Stages of Cancer Hyperplasia: proliferation of cells (many cells being produced) Dysplasia: abnormality in maturation of cells, expansion of immature cells In Situ Cancer: the tumor is found in the tissue it began in. Invasive Cancer: the tumor has spread into neighboring tissues.
How does a cell become cancerous? Certain genes (genetic codes) are mutated (altered) and no longer work properly. Two types of genes that regulate the cell cycle: 1. Proto-Ocogenes: Promotes cell division (the gas pedal) 2. Tumor Suppressor Genes: Inhibit cell division (the brakes)
Proto-oncogenes Stimulates cell division Produce proteins that signal the cell to divide Oncogene: Mutated form of the gene that over produces the stimulating protein The gas pedal is stuck down.
Tumor Suppressor Genes They inhibit cell division They produce an inhibitory protein for cell division Mutated genes may not produce the protein The brakes do not work.