what happens at the active site of an enzyme?

Answer 1

The definition from the answer above is correct.
Enzyme and substrates bind at the active site to make products.
E + S ⇌ ES → EP ⇌ E + P
where E = enzyme, S = substrates, and P = products

The active site is this little hole on the enzyme where the substrate goes into and does all this processing.
If you're more of a visual person, take a look at this
http://www.mun.ca/biology/scarr/F09-20b.jpg
and that pocket on the enzyme in the picture is the active site.
There's a better picture in my textbook but the link that I gave you seems as good. :)

Answer 2

First, the substrate fits into the active site, because it fits like a key in a lock .

The binding of functional groups of the substrate by functional groups within the active site tends to make the shape of the substrate similar to that of the transition state of the coming reaction.

If the reaction is an oxidation-reduction, then the active site also binds a cofactor like NAD+ or NADH near the substrate.

If the reaction is catalyzed by H+ or OH- or needs H2O, then functional groups in the active site donate these substances.

The configuration of functional groups in the active site ensure that reactive species attack the substrate from the side(s) that will lead to the wanted enantiomer, in case the product is asymmetric (chiral).

Answer 3

The active site of an enzyme contains the catalytic and binding sites. The structure and chemical properties of the active site allow the recognition and binding of the substrate.