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How do cells know when to stop dividing? contact inhibition
cancerous cells have lost this inhibition
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