Protein folding helpers What is the primary role of molecular chaperones during and after translation of a new polypeptide?

Introduction / Context:
Molecular chaperones are ubiquitous proteins that assist other proteins in achieving functional three-dimensional structure. While many polypeptides can fold spontaneously, crowded cytoplasmic conditions and complex topologies often require chaperone assistance. This is central to understanding proteostasis, stress responses, and biotechnology expression systems.

Given Data / Assumptions:

• New polypeptides emerge from ribosomes as linear chains.
• Correct tertiary structure is required for function.
• Chaperones do not encode sequence information; they prevent misfolding/aggregation.

Concept / Approach:

Chaperones (e.g., DnaK/DnaJ/GrpE, GroEL/GroES in bacteria; Hsp70/Hsp60 families) bind exposed hydrophobic regions to prevent aggregation, promote productive folding cycles, and sometimes refold stress-denatured proteins. They do not generally degrade proteins (that is the role of proteases) or recruit RNA polymerase or ribosomes to nucleic acids.

Step-by-Step Solution:

Verification / Alternative check:

Classic experiments show GroEL/GroES “cage” refolding of substrate proteins; loss of chaperones increases inclusion body formation in recombinant expression, confirming the functional role.

Why Other Options Are Wrong:

• Ribosome/mRNA or RNAP/DNA binding: Initiation factors and sigma factors mediate these, not chaperones.
• Degradation: ATP-dependent proteases (Lon, Clp) perform quality control degradation.
• Peptidyl transferase: Catalyzed by rRNA (ribozyme) in the 50S subunit, not by chaperones.

Common Pitfalls:

• Assuming chaperones “know” the final structure. They stabilize intermediates and promote correct folding but the sequence encodes the structure.

Final Answer:

Aid a newly synthesized polypeptide in folding to its proper shape