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| Oncogenes |
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| Growth and division of normal cells are regulated by control mechanisms. One such control mechanism is contact inhibition. As a result of multiplication, the cells become crowded and come in contact with one another. This surface contact checks movement and division of cells. Therefore, the genes which control these processes are turned off. In the case of cancer cells, the mechanism of contact inhibition does not function. The cells continue to divide, forming a tissue mass called tumour. The cancer cells may invade other tissues and cause tumours in them also. Thus, cancer is a differentiation related disease. |
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| Cancer is caused by viruses and mutagens such as radiation and chemicals. All these factors alter (activate) the proto-oncogenes. Altered proto-oncogenes are called oncogenes. Alteration may involve breaking into fragments, amplification or shifting to a new chromosomal location. Intact genes control normal growth and development of cells. Alteration in genes leads to the formation of abnormal proteins, change in the gene environment, and suspension of the mechanisms that control cell division. As a result of these changes, cell division goes uncontrolled, leading to the formation of malignant cells. |
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| fig. 24.1 - Oncogenes |
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Developoment and Differentiation
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