General Pathology — MCQs
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A 16-year-old girl presents with bowel obstruction. Laparotomy reveals markedly enlarged para-aortic lymph nodes. Biopsy of the lymph nodes exhibits a diffuse neoplastic infiltrate of small, round lymphocytes with a "starry sky" appearance on low power. The cytoplasm of some of the lymphocytes is vacuolated and fat stains are positive. What immunophenotypic or cytogenetic abnormality would you expect in the neoplastic cells?
Which of the following is NOT true about apoptosis?
A 52-year-old woman loses her right kidney following an automobile accident. A CT scan of the abdomen 2 years later shows marked enlargement of the left kidney. The renal enlargement is an example of which of the following adaptations?
Which type of immune response is responsible for caseation necrosis in TB?
What is the most important role of bradykinin in acute inflammation?
Which protein does Cytochrome C interact with to initiate apoptosis?
Which of the following is false regarding reversible cell injury?
Which of the following is a congenital deformity?
Familial amyloidotic polyneuropathy is due to amyloidosis of nerves caused by the deposition of which protein?
Which of the following statements about p53 is FALSE?
General Pathology Indian Medical PG Practice Questions and MCQs
Question 71: A 16-year-old girl presents with bowel obstruction. Laparotomy reveals markedly enlarged para-aortic lymph nodes. Biopsy of the lymph nodes exhibits a diffuse neoplastic infiltrate of small, round lymphocytes with a "starry sky" appearance on low power. The cytoplasm of some of the lymphocytes is vacuolated and fat stains are positive. What immunophenotypic or cytogenetic abnormality would you expect in the neoplastic cells?
- A. Positive non-specific esterase stain
- B. Positive specific esterase stain
- C. Low leukocyte alkaline phosphatase score
- D. t(8;14) translocation (Correct Answer)
Explanation: ### Explanation The clinical presentation and histopathology described are classic for **Burkitt Lymphoma (BL)**. **1. Why the correct answer is right:** * **Clinical Presentation:** A young patient with an abdominal mass (para-aortic lymph nodes/bowel obstruction) is characteristic of the **sporadic form** of Burkitt Lymphoma. * **Morphology:** The "starry sky" appearance is the hallmark of BL, created by tingible body macrophages (the "stars") ingesting apoptotic debris amidst a sea of dark, neoplastic B-cells (the "sky"). * **Cytology:** The presence of cytoplasmic vacuoles that stain positive for fat (Oil Red O) is a specific diagnostic feature of BL cells. * **Cytogenetics:** BL is defined by the translocation **t(8;14)**, which moves the **c-MYC proto-oncogene** from chromosome 8 to the Ig heavy chain locus on chromosome 14 [1]. This leads to constitutive expression of c-MYC, a potent regulator of cell proliferation. **2. Why the incorrect options are wrong:** * **Options A & B (Esterase stains):** Non-specific and specific esterase stains are used in the diagnosis of **Acute Myeloid Leukemia (AML)**, specifically to differentiate monocytic (NSE positive) from granulocytic lineages. They have no role in lymphoma diagnosis. * **Option C (Low LAP score):** A low Leukocyte Alkaline Phosphatase (LAP) score is a classic finding in **Chronic Myeloid Leukemia (CML)**, used to distinguish it from a leukemoid reaction (where the score is high). **3. High-Yield Facts for NEET-PG:** * **Variants:** Endemic (African/Jaw), Sporadic (Abdominal), and Immunodeficiency-associated (HIV). * **Virus Association:** Strongly linked with **Epstein-Barr Virus (EBV)**, especially the endemic variant. * **Immunophenotype:** CD19+, CD20+, CD10+, and **BCL-6+** (Germinal center origin). Notably, it is **BCL-2 negative** [1]. * **Proliferation:** It has one of the highest proliferation rates (Ki-67 index approach 100%). **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 563-564.
Question 72: Which of the following is NOT true about apoptosis?
- A. Inflammation is present (Correct Answer)
- B. Chromosomal breakage occurs
- C. Clumping of chromatin is observed
- D. Cell shrinkage is a characteristic feature
Explanation: **Explanation:** Apoptosis is a form of **programmed cell death** designed to eliminate unwanted cells without eliciting a host response. The hallmark feature that distinguishes apoptosis from necrosis is the **absence of inflammation** [3]. **Why Option A is the correct answer:** In apoptosis, the cell membrane remains intact, and the dying cell is rapidly fragmented into **apoptotic bodies**. These bodies are immediately recognized and phagocytosed by neighboring cells or macrophages [3]. Because the cellular contents (which include pro-inflammatory enzymes and DAMPs) are never leaked into the extracellular space, **no inflammatory response** is triggered [3]. In contrast, necrosis involves membrane rupture and the leakage of contents, which invariably leads to inflammation. **Analysis of other options:** * **Option B (Chromosomal breakage):** This is a key feature. Endonucleases cleave DNA into fragments of 180–200 base pairs, resulting in a characteristic **"step-ladder pattern"** on DNA electrophoresis [1]. * **Option C (Clumping of chromatin):** This is the most characteristic feature of apoptosis. Chromatin aggregates peripherally under the nuclear membrane (pyknosis). * **Option D (Cell shrinkage):** Unlike necrosis (where cells swell), apoptotic cells shrink, and the cytoplasm becomes dense and eosinophilic. **High-Yield NEET-PG Pearls:** * **Gold Standard for Detection:** The **TUNEL assay** is used to identify the DNA fragmentation characteristic of apoptosis. * **Morphological Hallmark:** Chromatin condensation. * **Biochemical Hallmark:** Activation of **Caspases** (Cysteine aspartate-specific proteases) [2]. * **Phosphatidylserine Flip:** In apoptotic cells, phosphatidylserine moves from the inner to the outer leaflet of the plasma membrane, acting as an "eat-me" signal for macrophages [3]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 101-102. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 64-65. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 67-69.
Question 73: A 52-year-old woman loses her right kidney following an automobile accident. A CT scan of the abdomen 2 years later shows marked enlargement of the left kidney. The renal enlargement is an example of which of the following adaptations?
- A. Atrophy
- B. Dysplasia
- C. Hyperplasia
- D. Hypertrophy (Correct Answer)
Explanation: ### Explanation The correct answer is **Hypertrophy**. **Mechanism and Concept:** When one kidney is removed (nephrectomy) or lost due to trauma, the remaining contralateral kidney undergoes **compensatory hypertrophy** [1]. Because nephrons are permanent cells and cannot undergo division (hyperplasia) to create new functional units, the existing cells increase in size to handle the increased metabolic and filtration workload [2]. This involves increased synthesis of structural proteins and organelles. In the kidney, this specifically involves the enlargement of the proximal convoluted tubule cells. **Analysis of Incorrect Options:** * **Atrophy (A):** This is a decrease in cell size and number, leading to a reduction in organ size. * **Dysplasia (B):** This refers to disordered growth and maturation of an epithelium (pre-neoplastic change). * **Hyperplasia (C):** This is an increase in the *number* of cells. While some minimal hyperplasia may occur in the collecting ducts, the predominant mechanism for renal enlargement in adults following nephrectomy is hypertrophy, as the total number of nephrons is fixed at birth [2]. **NEET-PG High-Yield Pearls:** 1. **Pure Hypertrophy:** Occurs in permanent cells (e.g., Cardiac muscle in hypertension, Skeletal muscle in exercise). 2. **Pure Hyperplasia:** Occurs in cells with regenerative capacity (e.g., Endometrial hyperplasia, Verruca vulgaris). 3. **Mixed (Hypertrophy + Hyperplasia):** Most common in stable/labile cells (e.g., Pregnant uterus, Benign Prostatic Hyperplasia). 4. **Compensatory Hypertrophy:** A classic example is the enlargement of the remaining kidney after unilateral nephrectomy [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 949-950. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 85-87.
Question 74: Which type of immune response is responsible for caseation necrosis in TB?
- A. Cell-mediated immunity (Correct Answer)
- B. Antibody mediated reaction
- C. Allergic reaction
- D. Immune complexes
Explanation: **Explanation:** The hallmark of *Mycobacterium tuberculosis* infection is the formation of granulomas with central **caseation necrosis**. This process is a classic example of a **Type IV Hypersensitivity reaction**, specifically driven by **Cell-Mediated Immunity (CMI)** [1], [4]. **Why Cell-Mediated Immunity is correct:** When *M. tuberculosis* enters the body, alveolar macrophages ingest the bacteria but are unable to kill them. These macrophages present antigens to **CD4+ T-lymphocytes (Th1 cells)**. The Th1 cells secrete **Interferon-gamma (IFN-γ)**, which activates macrophages, transforming them into "epithelioid cells" [2]. While this response aims to contain the infection, the prolonged release of lysosomal enzymes and reactive oxygen species by activated macrophages leads to tissue destruction, resulting in the cheese-like, acellular debris known as caseation necrosis [1], [3]. **Why other options are incorrect:** * **Antibody-mediated reaction (Type II):** This involves IgG or IgM antibodies binding to cell surface antigens. It plays no role in the destruction of intracellular pathogens like TB. * **Allergic reaction (Type I):** This is mediated by IgE and mast cells (e.g., asthma or anaphylaxis) and does not result in granuloma formation. * **Immune complexes (Type III):** This involves the deposition of antigen-antibody complexes in tissues (e.g., SLE or Glomerulonephritis), which is not the mechanism behind TB-induced necrosis. **NEET-PG High-Yield Pearls:** * **Cytokine of choice:** IFN-γ is the most critical cytokine for activating macrophages in TB [1]. * **Morphology:** Caseation is "cheese-like" macroscopically; microscopically, it appears as structureless, eosinophilic, granular debris [3]. * **Ghon Focus:** The initial site of parenchymal lung inflammation with caseation. * **Langhans Giant Cells:** Characteristic multinucleated cells formed by the fusion of epithelioid macrophages in TB granulomas [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 380-381. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 383-384. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 216-218.
Question 75: What is the most important role of bradykinin in acute inflammation?
- A. Increase in vascular permeability (Correct Answer)
- B. Vasodilatation
- C. Mediation of pain
- D. Bronchoconstriction
Explanation: **Explanation:** Bradykinin is a potent vasoactive nonapeptide derived from the kinin system [1]. During acute inflammation, Hageman factor (Factor XII) activation triggers the conversion of prekallikrein to kallikrein, which then cleaves high-molecular-weight kininogen (HMWK) to produce bradykinin. **1. Why "Increase in Vascular Permeability" is the correct answer:** While bradykinin performs multiple functions, its **most significant role** in the context of acute inflammation is the **increase in vascular permeability** [1], [2]. It acts directly on endothelial cells (via B2 receptors), causing endothelial cell contraction and the formation of intercellular gaps in post-capillary venules [2]. This leads to protein-rich fluid leakage (exudate) and subsequent edema, a hallmark of the inflammatory response. **2. Analysis of Incorrect Options:** * **B. Vasodilatation:** Bradykinin does cause arteriolar dilation (mediated by nitric oxide release); however, this is secondary to its role in increasing permeability in the hierarchy of inflammatory mediators [1]. * **C. Mediation of Pain:** Bradykinin is a well-known mediator of pain (along with prostaglandins), but this is a sensory effect rather than a primary structural driver of the acute inflammatory process [1], [2]. * **D. Bronchoconstriction:** While bradykinin causes extravascular smooth muscle contraction (like bronchospasm), this is a physiological effect seen in conditions like asthma or anaphylaxis, rather than a primary mechanism of general acute inflammation [1]. **Clinical Pearls for NEET-PG:** * **Short Half-life:** Bradykinin is rapidly inactivated by **Angiotensin-Converting Enzyme (ACE)** [1]. * **ACE Inhibitor Side Effect:** Patients on ACE inhibitors may develop a dry cough or angioedema due to the accumulation of bradykinin. * **C1 Esterase Inhibitor Deficiency:** Leads to Hereditary Angioedema due to uncontrolled bradykinin production. * **Triple Response of Lewis:** Bradykinin is involved in the "flare" and "wheal" components. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 100-101. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 187-188.
Question 76: Which protein does Cytochrome C interact with to initiate apoptosis?
- A. IL-10
- B. Bcl-2
- C. FADD
- D. Apaf-1 (Correct Answer)
Explanation: **Explanation:** The correct answer is **D. Apaf-1**. [1] This question tests knowledge of the **Intrinsic (Mitochondrial) Pathway** of apoptosis. When a cell undergoes stress or DNA damage, the permeability of the mitochondrial membrane increases, leading to the release of **Cytochrome C** into the cytosol. Once in the cytosol, Cytochrome C binds to a cytosolic protein called **Apaf-1** (Apoptotic Protease-Activating Factor-1). [2] This interaction, in the presence of dATP/ATP, leads to the formation of a wheel-like hexameric complex known as the **Apoptosome**. The apoptosome then recruits and activates **Caspase-9**, the initiator caspase of the intrinsic pathway, triggering the executioner caspase cascade. [1] **Why other options are incorrect:** * **IL-10 (A):** This is an anti-inflammatory cytokine that inhibits macrophage activation; it is not involved in the apoptotic signaling cascade. * **Bcl-2 (B):** This is an **anti-apoptotic** protein located in the mitochondrial membrane. It prevents apoptosis by inhibiting the release of Cytochrome C. [2] It does not interact with Cytochrome C once it is released. * **FADD (C):** Fas-Associated Death Domain is an adapter protein used in the **Extrinsic (Death Receptor) Pathway**. [3] It links the Fas receptor to **Caspase-8**, not Cytochrome C. **High-Yield Clinical Pearls for NEET-PG:** * **Initiator Caspases:** Caspase-9 (Intrinsic), Caspase-8 & 10 (Extrinsic). * **Executioner Caspases:** Caspase-3, 6, and 7 (Common to both pathways). [1] * **Bcl-2 Family:** Pro-apoptotic (Bax, Bak), Anti-apoptotic (Bcl-2, Bcl-xL), Sensors/BH3-only (Bad, Bim, Bid). * **Morphological Hallmark:** Chromatin condensation (Pyknosis) is the most characteristic feature of apoptosis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 64-67. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, p. 310. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, p. 67.
Question 77: Which of the following is false regarding reversible cell injury?
- A. Detachment of ribosomes from the endoplasmic reticulum (ER)
- B. Breakdown of plasma membrane (Correct Answer)
- C. Hydropic change
- D. Accumulation of myelin figures in the cytoplasm
Explanation: ### Explanation In pathology, the hallmark of **reversible cell injury** is the cell's ability to return to homeostasis if the stimulus is removed [1]. The transition to **irreversible injury** (cell death) is defined by two critical phenomena: the inability to reverse mitochondrial dysfunction and **profound disturbances in membrane function.** [1] **Why Option B is the Correct Answer:** The **breakdown of the plasma membrane** is a definitive sign of **irreversible cell injury** (necrosis) [1]. In reversible injury, the plasma membrane may show alterations like blebbing or loss of microvilli, but its structural integrity remains intact [1]. Once the membrane is breached, intracellular contents (like enzymes and proteins) leak into the extracellular space, and calcium influxes into the cell, triggering the final pathways of cell death. **Analysis of Incorrect Options:** * **A. Detachment of ribosomes:** This occurs due to swelling of the Rough Endoplasmic Reticulum (RER) caused by ATP depletion. It leads to a decrease in protein synthesis but is fully reversible [1]. * **C. Hydropic change:** Also known as cloudy swelling, this is the **earliest manifestation** of almost all forms of injury to cells [1]. It results from the failure of energy-dependent Na+/K+ ATPase pumps, leading to an accumulation of intracellular water [1]. * **D. Myelin figures:** These are whorled phospholipid masses derived from damaged cell membranes [1]. While they are more prominent in irreversible injury, they **begin to appear** during the reversible stage as organelles start to undergo mild damage [1]. **NEET-PG High-Yield Pearls:** * **Light Microscopy:** The first sign of reversible injury is **cellular swelling** (hydropic change) [1]. * **Electron Microscopy:** The first sign of reversible injury is **blebbing** of the plasma membrane and **mitochondrial swelling** [1]. * **Point of No Return:** The appearance of **large, flocculent (amorphous) densities** in the mitochondrial matrix is a classic sign of irreversible injury. * **Clinical Correlation:** Serum markers (e.g., Troponin in MI, ALT/AST in hepatitis) are detectable in blood only because of the **plasma membrane breakdown** associated with irreversible injury [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 49-62.
Question 78: Which of the following is a congenital deformity?
- A. Potter sequence
- B. Congenital talipes equinovarus (CTEV) (Correct Answer)
- C. Congenital heart disease
- D. Cleft lip
Explanation: In pathology and embryology, it is crucial to distinguish between different types of congenital anomalies: **Malformations, Deformations, Sequences, and Disruptions.** [1] ### **Explanation of the Correct Answer** **B. Congenital talipes equinovarus (CTEV):** This is a classic example of a **Deformation**. A deformation is an abnormality in form, shape, or position caused by **mechanical forces** acting upon a normally developing structure [1]. In CTEV (clubfoot), extrinsic factors like uterine constraint (e.g., oligohydramnios or multiple gestations) exert pressure on the developing fetal foot, leading to the deformity [1]. ### **Analysis of Incorrect Options** * **A. Potter sequence:** This is a **Sequence**, not a primary deformity. A sequence refers to a pattern of multiple anomalies derived from a single known prior anomaly or mechanical factor [1]. In Potter sequence, the primary event is renal agenesis, which leads to oligohydramnios, subsequently causing secondary features like flattened facies and pulmonary hypoplasia [1]. * **C. Congenital heart disease:** This is a **Malformation** [2]. Malformations are intrinsic abnormalities occurring during the period of organogenesis (weeks 3–8) due to an inherently abnormal developmental process (genetic or environmental). * **D. Cleft lip:** This is also a **Malformation** [2], resulting from the failure of the maxillary and medial nasal processes to fuse. ### **High-Yield Clinical Pearls for NEET-PG** * **Malformation:** Intrinsic error in morphogenesis (e.g., Polydactyly, Syndactyly) [1]. * **Deformation:** Extrinsic mechanical force (e.g., Clubfoot, Hip dislocation) [1]. * **Disruption:** Secondary destruction of a previously normally formed organ/body part (e.g., **Amniotic bands** causing limb amputation) [1]. * **Sequence:** Multiple anomalies resulting from a single initiating event (e.g., **Pierre Robin sequence**) [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 460-462. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 92-93.
Question 79: Familial amyloidotic polyneuropathy is due to amyloidosis of nerves caused by the deposition of which protein?
- A. Amyloid associated protein
- B. Mutant Calcitonin
- C. Mutant Transthyretin (Correct Answer)
- D. Normal transthyretin
Explanation: **Explanation:** **Familial Amyloidotic Polyneuropathy (FAP)** is an autosomal dominant condition characterized by the systemic deposition of amyloid fibrils, primarily affecting the peripheral and autonomic nerves. **Why Mutant Transthyretin is correct:** Transthyretin (TTR) is a serum protein synthesized in the liver that normally transports thyroxine and retinol [1]. In FAP, a genetic mutation (most commonly **Val30Met**) leads to the production of a structurally unstable **mutant transthyretin**. This mutant protein misfolds and aggregates into amyloid fibrils (ATTR), which preferentially deposit in the endoneurium of peripheral nerves, leading to progressive neuropathy and cardiomyopathy [1]. **Analysis of Incorrect Options:** * **Amyloid Associated (AA) Protein:** This is derived from Serum Amyloid A (SAA) during chronic inflammatory states (e.g., Rheumatoid Arthritis, Tuberculosis). It causes **Secondary Amyloidosis**, typically involving the kidneys, liver, and spleen, rather than primary nerve involvement. * **Mutant Calcitonin:** Deposition of procalcitonin/calcitonin occurs in the stroma of **Medullary Carcinoma of the Thyroid**. It is a localized form of amyloidosis. * **Normal Transthyretin:** Deposition of wild-type (normal) transthyretin occurs in **Senile Systemic Amyloidosis**. This typically affects the hearts of elderly patients (restrictive cardiomyopathy) and does not usually present as familial polyneuropathy [1]. **High-Yield Clinical Pearls for NEET-PG:** * **ATTR:** Mutant TTR = Familial Amyloidotic Polyneuropathy; Wild-type TTR = Senile Systemic Amyloidosis [1]. * **AL (Amyloid Light Chain):** Most common systemic amyloidosis; associated with Multiple Myeloma (Plasma cell dyscrasias). * **Diagnosis:** All amyloids show **Apple-green birefringence** under polarized light after **Congo Red staining**. * **Abeta (Aβ):** Found in the cerebral plaques of Alzheimer’s disease. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 266.
Question 80: Which of the following statements about p53 is FALSE?
- A. It is present on chromosome 17.
- B. It causes cell cycle arrest in G1.
- C. It has a molecular weight of 53 KDa.
- D. Non-mutated wild-type p53 is associated with neoplasia in childhood. (Correct Answer)
Explanation: The **p53 protein**, often called the "Guardian of the Genome," is a tumor suppressor protein encoded by the *TP53* gene. [1] **Why Option D is False (The Correct Answer):** Wild-type (non-mutated) p53 acts as a powerful **tumor suppressor**. [1] It prevents neoplastic transformation by monitoring DNA damage and inducing repair or apoptosis. It is the **mutated** form of p53, or the loss of both alleles, that is associated with neoplasia. While *TP53* mutations are common in many cancers, the specific germline mutation of p53 leads to **Li-Fraumeni Syndrome**, characterized by a high incidence of various tumors (sarcomas, breast cancer, leukemia) at a young age. **Analysis of Other Options:** * **Option A:** The *TP53* gene is indeed located on the short arm of **chromosome 17 (17p13.1)**. [1] Deletions of this region are frequently seen in human cancers. * **Option B:** p53 primarily causes cell cycle arrest at the **G1-S checkpoint**. It achieves this by transcriptionally activating **p21**, a CDK inhibitor that prevents the phosphorylation of the Retinoblastoma (Rb) protein. [2] * **Option C:** The name "p53" is derived from its molecular mass; it is a protein weighing **53 kiloDaltons (KDa)**. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Mutation:** *TP53* is the most frequently mutated gene in human cancer (>50% of all cases). [1] * **Mechanism of Action:** p53 senses DNA damage via ATM/ATR kinases. It can trigger three outcomes: **Quiescence** (temporary arrest), **Senescence** (permanent arrest), or **Apoptosis** (via BAX/PUMA). [3] * **Degradation:** In healthy cells, p53 levels are kept low by **MDM2**, which targets it for degradation. * **HPV Association:** The E6 oncoprotein of High-risk Human Papillomavirus (HPV 16, 18) binds to and degrades p53, leading to cervical cancer. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 226-228. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 302-303. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 303-304.
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