Q.4 Protein that helps other proteins to fold correctly is
(A) chaperone
(B) proteasome
(C) ubiquitin
(D) desmosome
The correct answer is (A) chaperone.
Chaperone proteins assist other proteins in achieving their correct three-dimensional structure during or after synthesis, preventing misfolding or aggregation. This makes them essential for proper protein folding in cells.
Option Analysis
(A) Chaperone
Chaperones bind to unfolded or partially folded polypeptides, stabilizing them and guiding correct folding without becoming part of the final structure. They are crucial in stress conditions, often identified as heat shock proteins, and are key in CSIR NET topics on protein folding.
(B) Proteasome
The proteasome is a proteolytic complex that degrades ubiquitinated proteins, including misfolded ones, to maintain cellular homeostasis but does not assist in folding. It acts after folding fails, targeting damaged proteins for breakdown.
(C) Ubiquitin
Ubiquitin tags proteins for degradation by the proteasome via covalent attachment, regulating processes like the cell cycle but not promoting folding—in fact, it can destabilize folds. It signals removal, not correction.
(D) Desmosome
Desmosomes are cell-cell adhesion structures in tissues like skin, linking cadherins to intermediate filaments for mechanical strength, unrelated to protein folding.
Proteins must fold into precise 3D shapes to function, and the protein that helps other proteins fold correctly is the chaperone. This SEO-optimized guide breaks down the MCQ options for CSIR NET aspirants, focusing on protein folding mechanisms.
Role of Chaperones in Protein Folding
Chaperones assist nascent polypeptides from ribosomes, preventing aggregation and promoting native conformations using ATP hydrolysis in some cases like chaperonins (Hsp60/Hsp10). They stabilize folding intermediates, vital for cellular proteostasis.
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Bind hydrophobic regions of unfolded proteins.
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Facilitate refolding under stress (e.g., heat shock).
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Essential in ER for quality control.
Why Not Other Options?
Proteasomes degrade misfolded proteins post-ubiquitination. Ubiquitin marks for destruction. Desmosomes provide adhesion, not folding aid.
| Option | Primary Function | Relation to Folding |
|---|---|---|
| Chaperone | Assists correct folding | Direct helper |
| Proteasome | Protein degradation | Handles failures |
| Ubiquitin | Tagging for degradation | Destabilizes |
| Desmosome | Cell adhesion | None |
Master this for CSIR NET: chaperones ensure proteins fold correctly.
