BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Cysteine, by virtue of its ability to form disulfide bonds, plays a crucial role in protein structure and in protein-folding pathways.

Detailed explanation-2: -The other sulfur-containing amino acid, methionine, cannot form disulfide bonds.

Detailed explanation-3: -Disulfide bond formation generally occurs in the endoplasmic reticulum by oxidation. Therefore disulfide bonds are mostly found in extracellular, secreted and periplasmic proteins, although they can also be formed in cytoplasmic proteins under conditions of oxidative stress.

Detailed explanation-4: -Cysteines are by far the most abundant amino acid around disulfide bonds, placing the class SULFUR on top of the most abundant classes (even though methionine has the lowest relative frequency of all amino acids). Almost all these cysteines are disulfide bonded, preventing mis-pairing effects.