Which immunoglobulin class has a dimeric structure with a secretory component? igm iga ige igg?

The answer is IgA.  The immunoglobulin can occur as a monomer or dimer. The dimeric form is called secretory-IgA because it is also secreted by glands that produce saliva, tears, sweat, and in the lumen of the gastrointestinal tract. It is the most secreted Immunoglobulin.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products