DNA ligase
Molecular Biology · Biotechnology
Say it: dee-en-AY LY-gays
DNA ligase is an enzyme that links two pieces of DNA end to end, making a phosphodiester bond that seals a break in the sugar-phosphate backbone.
Also: DNA ligases, polynucleotide ligase
Definition
What is DNA ligase?
DNA ligase is an enzyme that closes breaks, or nicks, in the backbone of DNA. Where two DNA ends lie next to each other, it joins the 3' hydroxyl of one end to the 5' phosphate of its neighbor through a phosphodiester bond, the same bond that joins all the nucleotides in a strand. The reaction needs an energy source: ATP in eukaryotes, archaea and many viruses, and NAD+ in most bacteria.
Ligase is essential for DNA replication. The lagging strand is made in short pieces called Okazaki fragments, and once their RNA primers have been replaced with DNA, ligase seals the remaining gaps to create one continuous strand. It also performs the final sealing step of excision repair, and a dedicated ligase completes the rejoining of broken double strands. Human cells make several ligases, numbered I, III and IV, for these different tasks.
In biotechnology, DNA ligase is the glue of molecular cloning. After a gene and a plasmid are cut with the same restriction enzyme, their matching sticky ends pair up, and ligase, most often the version from the bacteriophage T4, joins them permanently to make recombinant DNA. T4 ligase can also join blunt ends, though less efficiently.
Word parts
Where does the term “DNA ligase” come from?
- lig-
- to bind, to tieLatin ligare
- -ase
- enzymesuffix taken from diastase
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Related
Terms that go with it
- Okazaki fragmentAn Okazaki fragment is one of the short pieces of DNA made on the lagging strand during DNA replication and later joined into one continuous strand.
- DNA replicationDNA replication is how a cell copies all of its DNA before it divides, so that each daughter cell receives a complete genome.
- Restriction enzymeA restriction enzyme is a bacterial protein that cuts DNA at a specific short sequence, making it a basic tool for cutting and joining DNA.
- PlasmidA plasmid is a small, usually circular DNA molecule that copies itself independently of the main chromosome, found mostly in bacteria.
- Molecular cloningMolecular cloning is a set of laboratory methods for inserting a specific DNA fragment into a vector and copying it many times inside host cells.
- Recombinant DNARecombinant DNA is DNA made in the laboratory by joining pieces of DNA from different sources, often different species, into one molecule.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 14.4 DNA Replication in Prokaryotes
- OpenStax Biology 2e, 17.1 Biotechnology
- NCBI MeSH: DNA Ligases
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