What type of bonds are formed between two -SH groups during protein folding?

During protein folding, the formation of disulfide bonds occurs between two -SH (sulfhydryl) groups. Specifically, each -SH group is part of a cysteine amino acid, and when these groups come into proximity, they can undergo an oxidative reaction to form a covalent bond known as a disulfide bond (or bridge). This bond is represented as -S-S-, where two sulfur atoms are linked together.

Disulfide bonds play a critical role in stabilizing the three-dimensional structure of proteins, particularly those that are secreted from cells, as they help to maintain the protein's conformation under various conditions. The presence of disulfide bonds can significantly influence the stability and function of a protein, making them essential for the integrity of many extracellular proteins.

In contrast, other types of bonds mentioned do not apply in this context: hydrogen bonds are primarily responsible for secondary structures, ionic bonds involve interactions between charged groups, and peptide bonds link amino acids together in the primary sequence of a protein.