A genetic mutation occurs that changes a cysteine residue in the alpha-keratin protein into a methionine. The resulting mutant keratin will be more stable that the original, wildtype keratin. True or False?

False

Explanation:

Alpha-keratin protein consists of right-handed alpha-helix. Two individual strands of alpha-helix form coiled-coil which in turn represents its tertiary structure. The quaternary structure of an alpha-keratin protein is stabilized by cross-links. These cross-links are disulfide bonds formed by cysteine residues. The alpha keratin with a higher number of cysteine residues is harder and tougher.

Both methionine and cysteine are sulfur-containing amino acids. However, the absence of free - SH group in methionine does not allow this amino acid to form disulfide bonds. Cysteine has a free SH group to allow the formation of disulfide bonds. Therefore, a mutation in the alpha-keratin gene resulting in the substitution of cysteine with methionine will reduce the stability of the protein by reducing the number of disulfide cross-links