Carcinogens
புற்றுநோய் காரணிகள்
Cancer is not a sudden accident; it is a systematic breakdown of cell cycle regulation. If you think carcinogens are just 'bad chemicals,' you are failing the basics. They are the triggers that force a normal cell to bypass the G1/S checkpoint and enter uncontrolled mitosis.
The idea
Carcinogens are agents that induce neoplastic transformation in normal cells. They are classified into physical (e.g., ionizing radiation like X-rays and non-ionizing radiation like UV rays), chemical (e.g., tobacco smoke), and biological agents. These agents cause DNA damage, leading to mutations in proto-oncogenes and tumor suppressor genes. This transformation results in the loss of contact inhibition, a hallmark of cancerous cells.
Why it matters
These agents cause mutations or damage to DNA, disrupting the regulatory genes that control cell division and differentiation.
NEET lens
NEET focuses on the classification of carcinogens. Memorize the specific examples: X-rays and UV rays are physical; tobacco smoke is chemical. Do not confuse 'neoplastic transformation' with simple mutation; understand that it specifically leads to loss of contact inhibition. Expect match-the-following questions based on these categories.
Clinical significance
When carcinogens damage DNA, the cell loses its ability to undergo apoptosis. This leads to the formation of a malignant tumor, which invades surrounding tissues and spreads via metastasis. Without functional tumor suppressor genes like p53, the body cannot halt the proliferation of these neoplastic cells.
Introduction
Carcinogens are physical, chemical or biological agents that cause transformation of normal cells into cancerous (neoplastic) cells.
Core concept
Types (NCERT): physical — ionising radiations like X-rays and gamma rays, and non-ionising radiations like UV, which cause DNA damage leading to neoplastic transformation; chemical — chemical carcinogens in tobacco smoke are the major cause of lung cancer; biological — cancer-causing viruses called oncogenic viruses have genes called viral oncogenes. Several genes called cellular oncogenes (c-onc) or proto-oncogenes are present in normal cells; when activated under certain conditions, they can lead to oncogenic transformation of cells.
Go deeper
Cancer arises from mutations that disturb the normal control of cell growth and division. Proto-oncogenes are normal genes that become cancer-causing (oncogenes) when mutated or overactivated.
From Class 10
Smoking, too much sun and some viruses can damage the DNA of our cells. Substances that do this are called carcinogens.