Sort:  

Proteins are not just solid blobs inside of a cell. They are more like a machine, they move, and those movements in-turn lead to the binding of substrates and or chemistry performed by them. Proteins are often times subdivided into several different sections (called domains) with flexible regions (they can actually move in solution freely, the wiggle around) that link them together. Often times these different domains can perform separate functions, so they actually end up being complex machines with multiple working and moving parts.