Q.How is a cancerous cell different from a normal cell?

Concept and Intuition

p53 is a key tumor-suppressor protein that monitors cells for DNA damage. When damage is detected, p53 can pause the cell cycle to allow repair, or if the damage is too severe, push the cell towards programmed cell death (apoptosis) — preventing a damaged, potentially cancer-prone cell from dividing further. Because this activity actively protects the genome's integrity by stopping tumor-forming cells from propagating, p53 earned its well-known protective nickname.

Step-by-Step Solution

1. Confirm the assertion: p53 is indeed widely referred to with a protective, 'guardian'-style nickname reflecting its tumor-suppressing role — TRUE.
2. Confirm the reason: p53 inhibits tumor development by halting the cycle or triggering apoptosis of damaged cells — TRUE, and this is a well-established mechanism. …

Concept and Intuition

Tumours/cancers are broadly divided into solid tumours, which form a discrete lump of

abnormal tissue (e.g., carcinomas arising from epithelial tissue, sarcomas from connective

tissue, and lymphomas typically forming solid masses in lymph nodes), and

"liquid tumours," a term specifically used for blood cancers like leukemia, where

malignant white blood cells proliferate and circulate freely within the blood and bone

marrow rather than clumping into a solid mass.

Step-by-Step Solution

1. Carcinoma arises from epithelial cells and forms a solid tumour mass — not a liquid tumour.
2. Sarcoma arises from connective/mesenchymal tissue and also forms a solid tumour mass — not a liquid tumour.
3. Leukemia is a cancer of the blood-forming cells (usually white blood cell precursors) …

Concept and Intuition

Cancers are classified by the type of tissue in which they originate, and this classification directly gives their names:

• Carcinomas arise from epithelial tissue (the lining of organs, skin, glands) — the most common category of human cancers (e.g. breast, lung, colon cancers).
• Sarcomas arise from connective and supporting tissues such as bone, cartilage, fat, and muscle.
• Lymphomas arise from cells of the lymphatic system (lymph nodes, lymphoid tissue).
• Leukemias arise from blood-forming (haematopoietic) cells in the bone marrow, leading to abnormal proliferation of white blood cells in the blood.

Step-by-Step Solution

1. A) Carcinoma → epithelial tissues, item II.
2. B) Sarcoma → connective tissues, item III.
3. C) Lymphoma → lymphatic system, item I.
4. D) Leukemia → bone marrow, item IV. …

Concept and Intuition

When a piece of chromosome 9 (carrying the ABL gene) and a piece of chromosome 22 (carrying the BCR gene) are reciprocally exchanged, the resulting abnormally short chromosome 22 is called the Philadelphia chromosome. The fused BCR-ABL gene product is a constitutively active tyrosine kinase that drives uncontrolled proliferation of myeloid blood cells, causing Chronic Myelogenous Leukemia (CML).

Step-by-Step Solution

1. Recognize the 9;22 translocation as the classic Philadelphia chromosome abnormality.
2. Recall its disease association: CML, a cancer of myeloid blood cell lineage. …

Concept and Intuition

Tumour naming in oncology reflects the embryonic/tissue origin of the cancer cells. Epithelial tissues (skin, glandular tissue, linings of organs) give rise to carcinomas — the most common category of human cancers (e.g., lung, breast, colon cancers are mostly carcinomas).

Step-by-Step Solution

1. Sarcoma (option A) — arises from mesenchymal/connective tissue (bone, muscle, cartilage) — not epithelial.
2. Carcinoma (option B) — arises from epithelial tissue — matches the question. …

Concept and Intuition

Anticancer (antineoplastic) drugs typically target rapidly dividing cells by interfering with DNA replication or nucleotide synthesis. Methotrexate is a classic antimetabolite that structurally mimics folic acid, competitively inhibiting the enzyme dihydrofolate reductase, thereby starving cells of the reduced folates needed for purine/thymidylate synthesis — this selectively damages fast-dividing cancer cells and is widely used in chemotherapy regimens.

Step-by-Step Solution

1. Hetrozen (A, diethylcarbamazine citrate) is an anti-filarial drug used to treat Wuchereria/filariasis, not cancer.
2. Aureomycin (B, chlortetracycline) is a broad-spectrum antibiotic, not an anticancer drug. …

Concept and Intuition

Medical terminology built from Greek/Latin roots is common in biology exams — recognising the root "onco-" (tumour/bulk) immediately identifies the subject as tumours/cancer, distinct from other "-ology" terms like osteology (bones), odontology (teeth), or ornithology (birds).

Step-by-Step Solution

1. Break down the word: "onco-" = tumour/mass, "-logy" = study of. …

Concept and Intuition

Cancer-related genes fall into two broad categories: oncogenes (whose overactivity/gain-of-function promotes uncontrolled cell division) and tumour suppressor genes (whose normal function restrains cell division/promotes apoptosis, so their loss-of-function permits cancer). p53 (guardian of the genome, triggers apoptosis/cell cycle arrest on DNA damage) and pRB (restrains the G1-to-S transition by binding E2F transcription factors) are the two most classic tumour suppressor examples taught in this context.

Step-by-Step Solution

1. p53 monitors DNA integrity and halts the cell cycle or triggers apoptosis when damage is detected — loss of this function (as through mutation) removes a critical brake on tumour growth, which is exactly the hallmark of a tumour suppressor gene, not an oncogene.
2. pRB (retinoblastoma protein) normally binds and inhibits E2F transcription factors, preventing premature entry into S-phase; when pRB is lost/mutated, this brake fails, again characteristic of a tumour suppressor. …

Concept and Intuition

Cancer treatment often combines local approaches (surgery to remove the primary tumour, radiotherapy targeted at the tumour site) with systemic approaches (chemotherapy, immunotherapy) that travel through the bloodstream and can reach cancer cells that have metastasized to distant parts of the body — this is exactly why they are used in combination with local treatment. Separately, chemotherapeutic drugs are generally cytotoxic to all rapidly dividing cells, not just cancer cells; this non-specificity produces well-known side effects such as hair loss (from destruction of hair follicle cells), nausea, and anaemia.

Step-by-Step Solution

1. Evaluate Assertion (A): Chemotherapy and immunotherapy are indeed used precisely because they act systemically and can reach and destroy cancer cells that have spread beyond the original tumour site — TRUE.
2. Evaluate Reason (R): Chemotherapy drugs do cause side effects like hair loss, because they also damage rapidly dividing normal cells such as those in hair follicles — TRUE as a standalone fact. …

Concept and Intuition

Carcinogens are chemical, physical or biological agents that cause cancer by damaging DNA or disrupting cellular regulation. Coal tar was historically the very first substance linked to cancer causation — soot exposure in chimney sweeps was linked to scrotal cancer by Percival Pott in the 18th century. Later chemists isolated the actual carcinogenic compound from coal tar/soot: 3,4-benzopyrene (benzo[a]pyrene), a polycyclic aromatic hydrocarbon that intercalates into DNA and forms bulky adducts causing mutations. 4-aminobiphenyl and 2-naphthylamine are aromatic amine carcinogens linked to industrial dye/rubber exposure and bladder cancer, not coal tar specifically. Nitrosodimethylamine is a nitrosamine carcinogen found in tobacco and some foods, not the classic coal-tar agent.

Step-by-Step Solution

1. Recall that coal tar was the first chemically-linked source of cancer historically studied.
2. The specific carcinogenic compound isolated from coal tar is a polycyclic aromatic hydrocarbon. …

Concept and Intuition

A cancer cell is defined by the breakdown of the normal controls that keep tissue architecture and division in check:

• Cell adhesion: normal epithelial cells stick to their neighbours via adhesion proteins such as cadherins. Cancer cells characteristically down-regulate these proteins (loss of E-cadherin is a hallmark of the epithelial-to-mesenchymal transition that lets cancer cells invade and metastasize).
• Cell-cycle checkpoints: the G1 checkpoint is guarded by the tumour-suppressor protein $P^{53}$, which senses DNA damage and can arrest the cycle or trigger apoptosis. Loss of $P^{53}$ function is one of the most common events in human cancer.
• Contact inhibition: normal cells stop dividing once they touch their neighbours and cover a surface (contact inhibition). This is precisely what cancer cells lose — they keep piling up and dividing regardless of contact, which is why cancer cells 'show' the absence of contact inhibition, not the phenomenon itself.
• Benign vs malignant: a benign tumour stays localized and is relatively harmless; a malignant tumour is invasive, can metastasize, and is by definition the harmful, life-threatening form. So calling malignant tumours 'harmless' is a direct contradiction of the definition.
• Retinoblastoma protein ($p^{RB}$): another classical tumour-suppressor that normally restrains the cell cycle at the G1/S transition; its loss of function (as in retinoblastoma and many other cancers) removes this brake, letting cells divide uncontrolled.

Step-by-Step Solution

1. (i) Cadherins hold normal cells together and are lost in cancer cells — TRUE. …