Question

Hair straighteners use heated plates to temporarily straighten, flatten hair. This is because they:

• A. Denature proteins by changing the pH
• B. Denature proteins by disrupting hydrogen bonds and disulphide bonds
• C. Disrupt the amino acid sequence of hair protein
• D. Convert globular protein into fibrous proteins

Answer 1

The correct option is B Denature proteins by disrupting hydrogen bonds and disulphide bonds

Hair straighteners use heated air to temporarily straighten, flatten hair by disrupting the hydrogen bonds (H-bonds) and disulphide bonds. The hair protein called keratin exists in the form of a helix. These helices are stabilised by H-bonds and disulphide bonds. As heat from hot plates is applied on the curly hair, the H-bonds and disulphide bonds are broken down. The hair becomes straightened due to the shape of the flat plate. As the plates are withdrawn, the H-bonds and disulphide bonds renature or form so as to maintain the ‘straight’ form. The straightening is largely temporary because, over time, the hydrogen bonds and disulphide bonds form to restore the original conformation and exposure to moisture can make the proteins renature and curl up again.