The second option is the best answer.
Proteins are complex polymers of amino acids. They are folded into 3 dimensional structures . This folding defines not only the size and shape of the protein, but also its function.
The folding of a protein allows for interactions between amino acids that may be distant from each other in the primary sequence of the protein. In enzymes, some of these amino acids form a site in the structure that catalyzes the enzymatic reaction. This site is called the active site.
