Biology Biomolecules NUMS 2024
PMDC Verified Question 22 of 142
Rebounding is process of straightening the curly hairs, which bond is targeted by oxidizing agents used during the process?
A
Peptide Bond
B
Ionic bond
C
Disulphide bridge
D
Hydrogen bond
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Disulphide bridge
Concept:

The macroscopic shape of human hair is determined by permanent covalent cross-links within the keratin protein structure.

Solution:

  • Hair is composed of keratin, which contains a high proportion of the sulfur-containing amino acid Cysteine.


  • When two distant Cysteine residues align, they form strong covalent bonds called Disulphide bridges (S-S bonds). These rigid bridges pull the hair strand into permanent physical curls or waves.


  • Chemical hair straightening (rebounding or perming) utilizes reducing agents to purposefully break these specific Disulphide bridges. The hair is pulled straight, and then oxidizing agents are applied to re-form the bonds in the new, straight configuration.


Why other options are incorrect:

  • Hydrogen bonds: These are weak and are broken simply by wetting the hair (which is why wet hair hangs straight), but they reform immediately upon drying. They don't require harsh chemical oxidizing agents.


  • Peptide bonds: Breaking these would completely dissolve and destroy the entire protein backbone, dissolving the hair entirely rather than just straightening it.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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