Molecular Pathology Practice Questions

Q: Which of the following vitamins is required for post-translational modification?

Vitamin C. **Explanation:** **Correct Answer: D. Vitamin C** Vitamin C (Ascorbic acid) is a critical cofactor for the enzymes **prolyl hydroxylase** and **lysyl hydroxylase**. These enzymes are responsible for the **hydroxylation** of proline and lysine residues in pre-procollagen chains. This hydroxylation is a classic example of **post-translational modification**, occurring after the polypeptide chain has been synthesized. It allows for the formation of stable hydrogen bonds, which are essential for the triple-helix stability of collagen. Without Vitamin C, collagen fibers are defective and weak, leading to the clinical manifestation of Scurvy. **Analysis of Incorrect Options:** * **Vitamin B12 (Cobalamin):** Acts as a coenzyme for DNA synthesis (conversion of homocysteine to methionine) and myelin maintenance. It is involved in metabolic pathways rather than post-translational protein modification. * **Biotin (Vitamin B7):** Functions as a cofactor for **carboxylation** enzymes (e.g., Pyruvate carboxylase). While it modifies substrates, it is not primarily associated with the structural modification of proteins after translation. * **Beta-carotene:** A precursor to Vitamin A. Vitamin A is involved in gene transcription (via RAR/RXR receptors) and epithelial differentiation, but not direct post-translational modification of proteins. **High-Yield Clinical Pearls for NEET-PG:** * **Scurvy:** Characterized by "corkscrew hair," perifollicular hemorrhages, and bleeding gums due to defective collagen. * **Vitamin K:** Another high-yield vitamin involved in post-translational modification (**gamma-carboxylation** of Glutamic acid residues on Factors II, VII, IX, and X) [1]. * **Location:** Hydroxylation of collagen occurs within the **Rough Endoplasmic Reticulum (RER)**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 582-583, 624-625.

Question 1

What is the chromosomal abnormality associated with 100% recurrence of disease in Down's syndrome?

Accepted Answer

Trisomy 21 with translocation

Answer

Translocation of 15 and 21 chromosomes

Answer

Mosaic pattern

Answer

Non-disjunction

Question 2

Which of the following is true about metastatic calcification?

Accepted Answer

Calcification starts in mitochondria

Answer

Serum calcium level is normal

Answer

Occurs in dead or dying tissue

Answer

Occurs in damaged heart valves

Question 3

BRCA1 and BRCA2 genes are located on which chromosomes?

Accepted Answer

Chromosome 13 and 17

Answer

Chromosome 17 and 13

Answer

Chromosome 11 and 13

Answer

Chromosome 13 and 11

Question 4

What change is typically observed in mitochondria due to aging?

Accepted Answer

Decrease in both size and number

Answer

Decrease in size and increase in number

Answer

Decrease in number and increase in size

Answer

Increase in both size and number

Question 5

Which of the following vitamins is required for post-translational modification?

Accepted Answer

Vitamin C

Answer

Vitamin B12

Answer

Biotin

Answer

Beta-carotene

Question 6

In Langerhans Cell Histiocytosis, what is the characteristic abnormality seen?

Accepted Answer

Birbeck's granules

Answer

Foamy macrophages

Answer

Giant cells

Answer

Plasma cells

Question 7

Liquefactive necrosis is typically seen in which of the following conditions?

Accepted Answer

Ischemic necrosis of the brain

Answer

Ischemic necrosis of the heart

Answer

Ischemic necrosis of the intestine

Answer

Tuberculosis

Question 8

Which of the following stem cells are lowest in the hierarchy of specialization?

Accepted Answer

Totipotent stem cells

Answer

Unipotent stem cells

Answer

Multipotent uncommitted stem cells

Answer

Committed stem cells

Question 9

Which of the following is NOT involved in phagocytosis?

Accepted Answer

Pavementing of cells

Answer

Recognition and attachment

Answer

Engulfment

Answer

Killing and degradation

Question 10

A 40-year-old man is pulled from the ocean after a boating accident and resuscitated. Six hours later, the patient develops acute renal failure. Kidney biopsy reveals evidence of karyorrhexis and karyolysis in renal tubular epithelial cells. Which of the following biochemical events preceded these pathologic changes?

Accepted Answer

Decrease in intracellular pH

Answer

Activation of Na+/K+ ATPase

Answer

Decrease in intracellular calcium

Answer

Increase in ATP production

Molecular Pathology — MCQs

Molecular Pathology — MCQs

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