DNA ligation and cloning is a set of techniques used to join DNA fragments together and insert them into a vector—a carrier DNA molecule—for replication inside a host organism, typically bacteria. This allows scientists to produce large quantities of a specific DNA sequence.
How DNA Ligation and Cloning Works
- Preparing the Insert and Vector
Both the DNA fragment of interest (the insert) and the vector (usually a plasmid) are cut with the same restriction enzymes. This creates complementary sticky ends—short, single-stranded overhangs that can base-pair with each other.
- Ligation
The cut insert and vector are mixed together with DNA ligase, an enzyme that seals the sugar-phosphate backbone of DNA. The complementary sticky ends align, and the ligase forms covalent bonds, joining the insert permanently into the vector.
- Transformation
The ligated plasmid is introduced into competent bacterial cells through a process called transformation. This is often achieved by heat shock or electroporation, which makes the bacterial membrane temporarily permeable to DNA.
- Selection
The transformed bacteria are plated on agar containing an antibiotic. The plasmid carries an antibiotic resistance gene, so only bacteria that took up the plasmid survive. This creates colonies, each descended from a single cell containing the cloned DNA.
- Screening
Colonies are screened by colony PCR or restriction digestion to confirm they contain the correct insert. Positive colonies are grown in liquid culture to produce large amounts of the desired plasmid.
