DNA needs to be compiled into a protein in order to 'do' anything. DNA is the source code, proteins are the molecular machines built by the code. And every organism uses a similar compiler. So the DNA has to be put inside an organism before the DNA source code can be 'compiled' into a biological machine (a protein). Interestingly at the level of the compiler, almost every organism on Earth is capable of compiling most others' particular DNA into a protein (with a lot of exceptions).
Most purchased DNA that encodes a protein comes in the form of a bacterial 'virus' called a plasmid that can very easily be given to e coli - and it makes billions of copies of that DNA with very high fidelity in a few hours (https://en.wikipedia.org/wiki/Plasmid). This DNA can then be purified from that e coli in physically appreciable amounts and then be put into other organisms for ultimate usage. If you're purifying a chemical or a therapeutic the DNA is often put into yeast or e coli. If you're doing research, there are a number of 'model organisms' the DNA can be put into to supplement the genes already in the organism you're studying - including human cancer cells.
There are certain kinds of 'gene therapies' where the DNA is actually put into living human cells, often that have been harvested, and then put back into the person. This enables the genetic code for the new tools/proteins to be incorporated as a therapy.
The physical insertion of DNA into an organism is called "Transfection"
https://en.wikipedia.org/wiki/Transfection (or transduction, or transformation for various particulars).
Wonderful, thanks so much for the explanation. I think I knew that you had to get the DNA into an organism, but I had no idea how that could be done. The fact that the purchased DNA comes in the form of a virus that's ready to make lots more of that DNA is amazing.
Most purchased DNA that encodes a protein comes in the form of a bacterial 'virus' called a plasmid that can very easily be given to e coli - and it makes billions of copies of that DNA with very high fidelity in a few hours (https://en.wikipedia.org/wiki/Plasmid). This DNA can then be purified from that e coli in physically appreciable amounts and then be put into other organisms for ultimate usage. If you're purifying a chemical or a therapeutic the DNA is often put into yeast or e coli. If you're doing research, there are a number of 'model organisms' the DNA can be put into to supplement the genes already in the organism you're studying - including human cancer cells.
There are certain kinds of 'gene therapies' where the DNA is actually put into living human cells, often that have been harvested, and then put back into the person. This enables the genetic code for the new tools/proteins to be incorporated as a therapy.
The physical insertion of DNA into an organism is called "Transfection" https://en.wikipedia.org/wiki/Transfection (or transduction, or transformation for various particulars).
The general concept when applied to human health is called "Gene Therapy". https://en.wikipedia.org/wiki/Gene_therapy
The manipulation of DNA as a tool to understand the mechanisms of biology can be termed "Molecular Biology". https://en.wikipedia.org/wiki/Molecular_biology