Hi, if I wanted to break fructose down into its basic glucose
Yes, there's an enzyme that does that.
monomers,
Urm ... no, glucose is not a monomer of fructose, and fuctose is not a polymer.
what enzyme (or other?) would I use? And is this enzyme commercially available?
Yes.
Also, is there a way to convert glucose into a polysachharide such as amylose or amylopectin? Thank you.
Urm, yes, living things do, in fact, do this all the time. Commercially, however, building biopolymers is a little tricky. We do have a purely chemical maens of making short proteins and oligonucleotides, but large biopolymers are usually harvested from the natural sources.
A first year college biochemistry book will probably give you all the details you'd need, in the very first couple of chapters.