____ and ____ act as helix breakers due to their unique structure, which fixes the value of the C_α−N−C bond angle. A) Histidine, lysine B) Proline, hydroxyproline C) Arginine, lysine D) Serine, threonine E) Tyrosine, serine

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Proline and hydroxyproline both have a unique structure that introduces a kink in the polypeptide backbone, preventing the formation of a regular alpha helix. This "helix-breaking" property is due to the structure of the proline and hydroxyproline side chains, which form a cyclic structure that restricts rotation of the polypeptide backbone. In addition, the value of the C_α−N−C bond angle is fixed at approximately 60 degrees, which is different from the values observed for typical alpha helices.

____ and ____ Act as Helix Breakers Due to Their

and Act as Helix Breakers Due to Their