The first step is to isolate vector and donor DNA. If the donor is a bacterium, the main genomic DNA will be isolated. If it's a eukaryote, nuclear DNA is isolated. The vector DNA is commonly a bacterial plasmid. Plasmids must be separated from bacterial genomic DNA; this is commonly done by centrifugation.
Restriction enzymes are produced by bacteria to protect against infection by viruses. These enzymes act as scissors, cutting DNA at target nucleotide sequences. Restriction enzymes cut DNA into fragments small enough to be used in cloning with sticky ends that allow for joining of the vector and donor DNA.
The donor and vector DNA are combined. A DNA ligase enzyme will bind the sticky ends of the donor and vector DNA by creating phosphodiester bonds between the phosphate backbones of the two types of DNA.
The plasmid vector containing the donor DNA can enter a bacterial cell through simple transformation. Transformation occurs when a bacterial cell takes up DNA from the environment and incorporates it into the host genome. Then, the vector, along with the donor DNA, will be replicated by the bacterial cell along with its genome. In this way, the recombinant DNA is amplified.