Biology · Human Health and Diseases · NEET
A proto-oncogene is a NORMAL gene present in your healthy cells. It has a normal job in controlling cell growth. When it gets activated or mutated under certain conditions, it changes into an active cancer-causing form called an oncogene. So proto-oncogene = the safe sleeping version; oncogene = the dangerous woken version. NCERT calls proto-oncogenes 'cellular oncogenes (c-onc)'. For NEET, remember: proto-oncogene → (activation) → oncogene → oncogenic transformation.
Carcinogens are agents that change normal cells into cancerous (neoplastic) cells. NCERT lists three types. Physical carcinogens: ionising radiations like X-rays and gamma rays, and non-ionising radiation like UV. Chemical carcinogens: chemicals in tobacco smoke, which are a major cause of lung cancer. Biological carcinogens: oncogenic viruses. All of these damage DNA and lead to neoplastic transformation.
Viral oncogenes are cancer-causing genes carried by oncogenic viruses (cancer-causing viruses). Cellular oncogenes (c-onc), also called proto-oncogenes, are present inside our own normal cells. So the difference is the source: viral oncogenes come from a virus, while cellular oncogenes are already in our body and only cause cancer when activated. NEET has asked about both, so keep the two words separate.
Yes. NCERT clearly states that ionising radiations like X-rays and gamma rays AND non-ionising radiation like UV both cause DNA damage, which leads to neoplastic (cancerous) transformation. Students often think only ionising radiation is dangerous, but UV (non-ionising) is also a physical carcinogen. This is a common NEET trap.
Tobacco smoke contains chemical carcinogens. NCERT specifically says these chemicals in tobacco smoke have been identified as a major cause of LUNG cancer. So if a NEET question links tobacco to a cancer type, the answer is lung cancer, and tobacco acts as a chemical carcinogen (not physical, not biological).
Which of the following statements is not true for cancer cells in relation to mutations?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
c-onc stands for cellular oncogenes. NCERT uses c-onc as another name for proto-oncogenes — genes already present in normal cells that can cause cancer when activated.
Physical (ionising radiation like X-rays/gamma rays, and non-ionising UV), chemical (chemicals in tobacco smoke), and biological (oncogenic viruses). Together they cause neoplastic transformation of normal cells.
Oncogenic viruses are cancer-causing viruses. They carry cancer-causing genes called viral oncogenes. They are the biological carcinogens in the causes of cancer.
No. In a normal cell a proto-oncogene is not harmful — it helps control normal cell growth. It only becomes harmful (an oncogene) when it is activated under certain conditions, leading to oncogenic transformation.
Lung cancer. NCERT states the chemical carcinogens in tobacco smoke are a major cause of lung cancer.
