Concept:Heavy metals are profound cellular poisons because they target the fundamental architectural pillars of proteins.
Solution:- The 3D folding of many critical enzymes is maintained by strong covalent disulfide bridges between cysteine amino acids.
- Heavy metal ions (like \( \text{Hg}^{2+} \), \( \text{Pb}^{2+} \)) have an immense chemical affinity for the sulfur in these sulfhydryl (-SH) groups.
- When they bind to the sulfur, they physically rip apart the disulfide bridges, causing the protein to unfold. This ability to violently destabilize proteins leads to rapid cell death.
Why other options are incorrect:While heavy metals can indirectly affect all metabolism by destroying the enzymes involved, their direct, primary chemical mechanism of toxicity is the irreversible denaturation and destabilization of proteins, not specifically attacking fats, nucleic acids, or carbohydrates.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.