Read the 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. In our body, cell growth and differentiation is highly controlled and regulated. In cancer cells, there is breakdown of these regulatory mechanisms. Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth. Cancer cells appears to have lost this property. As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors.
Cancer-causing (oncogenic) viruses carry genes called:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Viral oncogenes
Agents that turn normal cells into cancer cells are called carcinogens. They may be physical (radiations), chemical (such as those in tobacco smoke) or biological. The biological agents are oncogenic viruses, which cause cancer through special genes they carry.
Option (1) Proto-oncogenes — Incorrect. Proto-oncogenes, also called cellular oncogenes (c-onc), are found in normal cells. They can lead to cancer when activated, but they are the cell’s own genes, not genes carried by viruses.
Option (2) Viral oncogenes — Correct. Oncogenic viruses carry viral oncogenes. When such a virus infects a cell, these genes can change the cell into a cancer cell.
Option (3) Interferon genes — Incorrect. Interferons are proteins made by virus-infected cells that protect nearby uninfected cells from viral infection. α-interferon is even used in cancer treatment to activate the immune system, so these genes fight disease rather than cause cancer.
Option (4) Viral coat protein genes — Incorrect. Coat protein genes code for the protein coat that encloses the genetic material of a virus. They build the virus particle; they are not the genes that turn host cells cancerous.
NCERT Extract:
Cancer – “… Causes of cancer : Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents. These agents are called carcinogens. … 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.”
Innate Immunity – “… (iv) Cytokine barriers : Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.”