96. Protein folding is highly cooperative. Which one of the following statement define
this cooperativity?
(a) If one protein unfolds, it forces a nearby protein to unfold too,
(b) If one proteins chain folds, it facilitates the folding of a nearby chain,
(c) Many molecules of polypeptides come together to fold at the same time,
(d) The protein chain completely unfolds if key interactions are broken in an “all or none”manner

Detailed Explanation:

Protein folding is a complex but highly coordinated process where a linear chain of amino acids adopts a specific 3D structure. This process is cooperative, meaning that it doesn’t occur in small, independent steps but rather in a highly synchronized manner.

What Does Cooperativity in Protein Folding Mean?

The cooperativity in protein folding refers to how multiple parts of the protein influence each other during the folding process. Once folding starts at one point, it accelerates folding in other regions, and if critical interactions are disrupted, the entire protein can rapidly unfold.

Correct Answer:

(d) The protein chain completely unfolds if key interactions are broken in an “all or none” manner

This describes cooperativity perfectly. In this model, once a critical threshold is passed—such as the disruption of a hydrogen bond or hydrophobic core—the whole structure collapses, rather than unfolding in segments. This is especially evident in small globular proteins.

 Why Other Options Are Incorrect:

• (a) talks about neighboring proteins, not intra-molecular folding.

• (b) refers to interactions between chains, not within one chain.

• (c) implies multiple polypeptides folding together, which doesn’t define cooperativity.