What part of an enzyme or antibody is involved in the chemical reaction?

The active site of an enzyme or antibody is the specific region where the chemical reaction occurs. This site has a unique three-dimensional shape and chemical environment that facilitates the binding of substrates or antigens. In enzymes, the active site is crucial for lowering the activation energy of a reaction, allowing the transformation of substrates into products efficiently. This selective interaction ensures that only specific molecules can fit and react at that site, which is essential for the enzyme's catalytic function.

In the context of antibodies, the active site corresponds to the region that binds to an antigen, leading to the neutralization or marking of the pathogen for destruction. Thus, the active site plays a critical role in the functionality of both enzymes and antibodies by directly participating in the chemical processes essential for biological functions.