What type of bond is primarily formed between two cysteine residues?

The bond primarily formed between two cysteine residues is known as a disulfide bond. Cysteine contains a thiol (-SH) group in its side chain, and when two cysteine residues come close together, their thiol groups can undergo oxidation. This reaction leads to the formation of a covalent bond called a disulfide bond (or linkage), where sulfur atoms from the two cysteine residues bond together to form a -S-S- bridge.

Disulfide bonds are significant in stabilizing the three-dimensional structure of proteins, particularly in extracellular environments where oxidative conditions favor their formation. By stabilizing folds and providing structural integrity, disulfide bonds contribute to the overall stability and functionality of proteins. This is particularly important in many secreted proteins and antibodies.

Other types of bonds mentioned, such as hydrogen bonds, ionic bonds, and peptide bonds, play different roles in protein structure:

• Hydrogen bonds are important for secondary structures like alpha helices and beta sheets.

• Ionic bonds contribute to interactions between charged side chains.

• Peptide bonds link amino acids together in the primary structure of proteins.

Thus, while those bonds are essential in various contexts, they do not specifically arise between cysteine residues, making the disulfide bond