And these are covalent bonds that exist within protein structures. And they play an important role in actually determining the three dimensional structure of our protein. So cysteine is structurally similar to Serene, except it has a thyl group. So Serene is polar and reactive in forming disulfide bridges. So if we compare these two, this is almost the same as this. The only difference is we replace the oxygen in this case with a sulfur in this case.