Barber Practice State Board Practice Exam

What element forms disulfide bonds between neighboring cysteine amino acids?

1. Sodium

2. Chlorine

3. Sulfur

4. Calcium

The correct answer is: Sulfur

Disulfide bonds are formed between cysteine amino acids through the interaction of sulfur atoms. Each cysteine contains a reactive thiol (-SH) group, and when two cysteine residues become oxidized, the sulfur atoms from their thiol groups form a covalent bond, resulting in a disulfide bond (–S–S–). This type of bond is crucial for stabilizing the tertiary and quaternary structures of proteins, contributing to the overall shape and functionality. The other elements listed do not have a role in the formation of disulfide bonds. Sodium and chlorine are not involved in covalent bonding in this context, as they are more likely to participate in ionic bonding. Calcium is primarily involved in other biological processes, such as muscle contraction and signal transduction, rather than in the formation of disulfide bonds. Thus, the correct choice is the element sulfur, which is fundamental to creating these important structural links between cysteine residues in proteins.