Q.19 Molecular chaperones are class of proteins that facilitate

• (A) the proper folding of newly synthesized proteins
• (B) unfolding of newly synthesized proteins
• (C) degradation of newly synthesized proteins
• (D) targeting of newly synthesized proteins

  Molecular chaperones are class of proteins that facilitate the proper folding of newly synthesized proteins, preventing aggregation in crowded cellular environments. This SEO-optimized article answers the MCQ: Molecular chaperones are class of proteins that facilitate (A) proper folding of newly synthesized proteins, (B) unfolding, (C) degradation, (D) targeting—crucial for biochemistry, cell biology, and biotechnology students studying protein quality control.

  Correct Answer: Option (A) Proper Folding of Newly Synthesized Proteins

  Molecular chaperones like Hsp70, Hsp90, GroEL/ES, and CCT/TRiC bind hydrophobic regions of nascent polypeptides emerging from ribosomes, preventing premature misfolding and aggregation.

  They utilize ATP-dependent cycles: Hsp70 captures extended chains cotranslationally; chaperonins (GroEL) provide isolated folding chambers; Hsp90 handles late-stage folding of signaling proteins. Chaperones never become part of final protein structure.

  Explanation of All Options

  Chaperones vs. other protein quality control systems:

  • (A) Proper folding: Correct. Primary function—stabilize folding intermediates, prevent aggregation.

  • (B) Unfolding: Incorrect. Some chaperones (Hsp104) disaggregate, but most promote folding, not unfolding.

  • (C) Degradation: Incorrect. Ubiquitin-proteasome handles misfolded proteins; chaperones attempt rescue first.

  • (D) Targeting: Incorrect. Chaperones aid folding for subsequent targeting; signal recognition particle (SRP) handles ER/mito targeting.

  Option	Protein System	Cellular Role	Chaperone Function?
  (A) Proper folding	Hsp70/GroEL	Nascent chain folding	Correct
  (B) Unfolding	Hsp104 (disaggregase)	Aggregate solubilization	Secondary role
  (C) Degradation	Ubiquitin-proteasome	Misfolded destruction	No
  (D) Targeting	SRP, TOM/TIM	Organelle import	Post-folding

  Biotechnology Relevance

  Chaperone co-expression boosts recombinant protein yields in E. coli/yeast (insulin from Q.5), prevents inclusion bodies during N-glycosylation engineering (Q.13), and supports hairy root protein production (Q.11)—directly enhancing your mammalian/microbial expression systems.