Tumor Formation <ul><li>Sometimes the normal control of mitosis in a cell fails </li></ul><ul><li>This cell divides into two </li></ul><ul><li>The two daughter cells divide to form four cells </li></ul><ul><li>Repeated divisions soon produce a mass of cells called tumor </li></ul><ul><li>This can happen in any organ </li></ul><ul><li>Tumors can grow to a large size and can spread to other parts of the body </li></ul><ul><li>The diseases caused by the growth of tumors are called cancer </li></ul>
Control of the Cell Cycle <ul><li>cell cycle proceeds on it’s own clock, but is regulated at certain checkpoints </li></ul>
breast cancer cell <ul><li>cells can become cancerous for several reasons: </li></ul><ul><li>- damage to DNA </li></ul><ul><li>- environmental exposure toxins; examples: *PCB’s--polychlorinated biphenyl *DDT--dichlor-diphenyl- trichlorethylene </li></ul><ul><li>- other cell control issues </li></ul><ul><li>- damaged proteins </li></ul><ul><li>- genetic factors </li></ul>
How do cells know when to stop dividing? contact inhibition <ul><li>cancerous cells have lost this inhibition </li></ul>
Features of cancer cells cell shape is easily distinguished from normal, healthy cells cancerous cells lose their attachment to neighboring cells cancer cells may have an unusual # of chromosomes cancer cells can go on dividing indefinitely , if they have an unlimited supply of nutrients they are said to be “immortal” metabolism may be drastically altered and the cell stops functioning in a constructive way
Oncogenesis, proto-oncogenes and tumor suppressor genes There are two types of genes necessary for normal control of cell division: 1. proto-oncogenes (start cell division and are essential for normal cell development) 2. tumor suppressor genes (switch off cell division) Oncogenes: these arise when these cell cycle control genes become mutated -- these mutations lead to uncontrolled cell division Ex: many cancers are initiated when there are mutations in tumor-suppressor genes p53 : this tumor suppressor gene encodes for a protein that halts the cell cycle so that DNA can be repaired before division
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