Which statement correctly pairs a chaperone type with its function?

Which statement correctly pairs a chaperone type with its function?

• A. Hsp70 binds nascent polypeptides; chaperonins GroEL/GroES provide an isolated folding chamber
• B. Hsp70 degrades misfolded proteins
• C. Chaperonins export proteins across membranes
• D. Hsp70 catalyzes disulfide bond formation

Answer: (A)

The main idea here is that different chaperone systems have distinct roles in helping proteins fold correctly. The pairing that fits best is: Hsp70 binds nascent polypeptides as they emerge from the ribosome, preventing aggregation and guiding initial folding; chaperonins GroEL and GroES provide an isolated folding chamber where the polypeptide can fold away from the crowded cytosol. Hsp70 acts early, recognizing exposed hydrophobic regions on newly synthesized or unfolded chains. Through ATP-driven binding and release, it stabilizes these segments and shields the chain from sticking to itself or other molecules, giving the polypeptide time to achieve its initial structure. Once partial folding occurs, the substrate can be handed off to other folding systems. GroEL and GroES form a stacked, barrel-shaped complex that creates a contained environment, the folding chamber. A misfolded or partially folded protein enters the chamber, the lid (GroES) closes, and inside the environment promotes proper folding by reducing the chance of premature aggregation. After a cycle powered by ATP, the chamber opens and the protein is released, often already closer to its correctly folded state. Why the other statements don’t fit: Hsp70’s main job is not degrading proteins—that role belongs to proteases and targeted degradation pathways. Chaperonins don’t export proteins across membranes; translocation uses dedicated membrane transport systems. And Hsp70 doesn’t catalyze disulfide bond formation; such bonds are formed by disulfide isomerases in specific cellular compartments.

The main idea here is that different chaperone systems have distinct roles in helping proteins fold correctly. The pairing that fits best is: Hsp70 binds nascent polypeptides as they emerge from the ribosome, preventing aggregation and guiding initial folding; chaperonins GroEL and GroES provide an isolated folding chamber where the polypeptide can fold away from the crowded cytosol.

Hsp70 acts early, recognizing exposed hydrophobic regions on newly synthesized or unfolded chains. Through ATP-driven binding and release, it stabilizes these segments and shields the chain from sticking to itself or other molecules, giving the polypeptide time to achieve its initial structure. Once partial folding occurs, the substrate can be handed off to other folding systems.

GroEL and GroES form a stacked, barrel-shaped complex that creates a contained environment, the folding chamber. A misfolded or partially folded protein enters the chamber, the lid (GroES) closes, and inside the environment promotes proper folding by reducing the chance of premature aggregation. After a cycle powered by ATP, the chamber opens and the protein is released, often already closer to its correctly folded state.

Why the other statements don’t fit: Hsp70’s main job is not degrading proteins—that role belongs to proteases and targeted degradation pathways. Chaperonins don’t export proteins across membranes; translocation uses dedicated membrane transport systems. And Hsp70 doesn’t catalyze disulfide bond formation; such bonds are formed by disulfide isomerases in specific cellular compartments.