Each element is made of only one kind of atom
In biotechnology, the process of introducing the foreing DNA into a cell by a virus is called transduction.Gene therapy is one of the purposes of this process.
Other types of enzymes can put atoms and molecules together. Breaking molecules apart and putting molecules together is what enzymes do, and there is a specific enzyme for each chemical reaction needed to make the cell work properly.
https://science.howstuffworks.com/life/cellular-microscopic/cell2.htm