Much like how a city's subway system keeps people moving (and city life running!), disulfide bonds are critical support systems for antibodies. They ensure stable, proper chain pairing between heavy and light chains, enabling the fully assembled four-chain antibody "Y" that we're so used to seeing. 

You could argue that heavy and light chains can still assemble via vast hydrophobic interfaces, but that's fleeting! Disulfides ensure these chains stay together through all that they encounter as they make their way to their target in the body.

Disulfide bonds are covalent (strong!) bonds that form post-translationally between the sulfur atoms of two cysteines. And while you might think it's a clear route from point A to point B, as you'll see below, that isn't always the case!