How do enzymes act as biological catalysts?
Enzymes are , and therefore have very specific structures suited to their functions. A protein is folded in a complex three dimensional manner which exposes some areas on the surface and hides others.
These exposed areas are called active sites. Only specific molecules that match the shape of an active site can bind to it, and once they do, the protein changes their shape, or adds a molecule etc. This is the function of enzymes in the body.
They act as biological catalyses because in order for certain reactions to proceed, enzymes must be present. What the enzymes then do is bind to the necessary molecules and make sure the reaction proceeds by breaking down molecules and making it easier for them to come together.
There is a specific enzyme to every reaction, due to the very special three dimensional shape, which is why we have many different types of enzymes that catalyze many different types of reactions in our bodies.
Enzymes, as biological catalysts also have an optimum temperature and pH range. They will work as long as their shape is intact. If the temperature or pH are too extreme, the enzyme risks losing its shape and thereby its function.