Read the following passage and answer the following questions:
Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the globe. More than a million Indians suffer from cancer and a large number of them die from it annually. The mechanisms that underlie development of cancer or oncogenic transformation of cells, its treatment and control have been some of the most intense areas of research in biology and medicine. Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth. Cancer cells appear to have lost this property. As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors. Transformation of normal cells into cancerous cells may be induced by carcinogens. Radiations cause DNA damage leading to neoplastic transformation. Cancer causing viruses called oncogenic viruses have genes called viral oncogenes. Cancer detection is based on biopsy and histopathological studies of the tissue and blood and bone marrow tests for increased cell counts in the case of leukemias. Techniques like radiography, CT and MRI are very useful to detect cancers of the internal organs. The common approaches for treatment of cancer are surgery, radiation therapy and immunotherapy.
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Normal cells of the body carry cellular oncogenes (c-onc), yet these cells need not turn cancerous.
Reason (R): Cellular oncogenes lead to oncogenic transformation of cells when they are activated under certain conditions.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are true and (R) is the correct explanation of (A).
Assertion (A): Normal cells of the body carry cellular oncogenes (c-onc), yet these cells need not turn cancerous. — True. A is about the presence of oncogenes in healthy cells. Genes called cellular oncogenes (c-onc) or proto oncogenes have been found in normal cells, and such cells live and divide normally.
Reason (R): Cellular oncogenes lead to oncogenic transformation of cells when they are activated under certain conditions. — True. R is about when these genes cause cancer. They lead to oncogenic transformation only after they are activated under certain conditions.
Why R explains A? Carrying a gene is not the same as using it. As long as the cellular oncogenes in a normal cell are not activated, they do not transform the cell. That is why a normal cell can carry c-onc and still not turn cancerous. So R is the correct explanation of A.
The passage speaks only of viral oncogenes carried by oncogenic viruses; it does not mention cellular oncogenes.
NCERT Extract:
Cancer – “… Ionising radiations like X-rays and gamma rays and non-ionizing radiations like UV cause DNA damage leading to neoplastic transformation. The chemical carcinogens present in tobacco smoke have been identified as a major cause of lung cancer. Cancer causing viruses called oncogenic viruses have genes called viral oncogenes. Furthermore, several genes called cellular oncogenes (c-onc) or proto oncogenes have been identified in normal cells which, when activated under certain conditions, could lead to oncogenic transformation of the cells.”