In molecular biology, DNA ligase is a specific type of enzyme, a ligase, () that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.

It plays a role in repairing single-strand breaks in duplex DNA in living organisms, but some forms ( such as DNA ligase IV ) may specifically repair double-strand breaks ( i. e. a break in both complementary strands of DNA ).

Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template ,, with DNA ligase creating the final phosphodiester bond to fully repair the DNA.

DNA ligase has applications in both DNA repair and DNA replication ( see Mammalian ligases ).

In addition, DNA ligase has extensive use in molecular biology laboratories for genetic recombination experiments ( see Applications in molecular biology research ).

Purified DNA ligase is used in gene cloning to join DNA molecules together to form recombinant DNA.

The mechanism of DNA ligase is to form two covalent phosphodiester bonds between 3 ' hydroxyl ends of one nucleotide, (" acceptor ") with the 5 ' phosphate end of another (" donor ").

A pictorial example of how a ligase works ( with DNA end | sticky end s )

* DNA ligase I: ligates the nascent DNA of the lagging strand after the Ribonuclease H has removed the RNA primer from the Okazaki fragments.

* DNA ligase II: alternatively spliced form of DNA ligase III found in non-dividing cells.

3-The mobile plasmid is nicked and a single strand of DNA is then transferred to the recipient cell.

This has been shown in experiments where the pilus are allowed to make contact, but then are denatured with SDS and yet DNA transformation still proceeds.

The transferred DNA can then be integrated into the recipient genome via homologous recombination.

All known forms of life are based on the same fundamental biochemical organisation: genetic information encoded in DNA, transcribed into RNA, through the effect of protein-and RNA-enzymes, then translated into proteins by ( highly similar ) ribosomes, with ATP, NADH and others as energy sources, etc.

Usually DNA damage, if too severe to repair, leads to programmed cell death, but if the programmed cell death pathway is damaged, then the cell cannot prevent itself from becoming a cancer cell.

According to the central dogma of molecular biology, when synthesizing a protein, a gene's DNA is transcribed into mRNA which is then translated into protein.

# From the hairpin loop, a DNA polymerase can then use it as a primer to transcribe a complementary sequence for the ss cDNA.

DNA polymerase then synthesizes a new strand of DNA by extending the 3 ' end of an existing nucleotide chain, adding new nucleotides matched to the template strand one at a time via the creation of phosphodiester bonds.

The 5 ′ end of the nicked strand is transferred to a tyrosine residue on the nuclease and the free 3 ′ OH group is then used by the DNA polymerase for new strand synthesis.

After inducing encystation in E. invadens, DNA replication increases initially and then slows down.

An exon is a sequence of DNA that is expressed ( transcribed ) into RNA and then translated into protein.

Progress in DNA sequencing, specifically mitochondrial DNA ( mtDNA ) and then Y-chromosome DNA advanced the understanding of human origins.

Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas, and then the chimpanzees ( genus Pan ) split off from the line leading to the humans ; human DNA is approximately 98. 4 % identical to that of chimpanzees when comparing single nucleotide polymorphisms ( see human evolutionary genetics ).

X-ray crystallography theoretically offered the opportunity to reveal the molecular structure of large molecules like proteins and DNA, but there were serious technical problems then preventing X-ray crystallography from being applicable to such large molecules.

This DNA is then transferred into an organism, giving it modified or novel genes.

The first transgenic ( genetically modified ) animal was produced by injecting DNA into mouse embryos then implanting the embryos in female mice.

This is accomplished by isolating and copying the genetic material of interest using molecular cloning methods to generate a DNA sequence containing the required genetic elements for expression, and then inserting this construct into the host organism.

In such circumstances then, " genome " describes all of the genes and information on non-coding DNA that have the potential to be present.

The DNA band can also be cut out of the gel, and can then be dissolved to retrieve the purified DNA.

The combined hormone-receptor complex then moves across the nuclear membrane into the nucleus of the cell, where it binds to specific DNA sequences, effectively amplifying or suppressing the action of certain genes, and affecting protein synthesis.

If DNA was the genetic material, then DNA from the labeled phage would have to enter the bacterial cells, and carry the radioactive phosphorus with it.

In the canonical Watson-Crick DNA base pairing, adenine ( A ) forms a base pair with thymine ( T ) and guanine ( G ) forms a base pair with cytosine ( C ).

Along with RNA and proteins, DNA is one of the three major macromolecules that are essential for all known forms of life.

Unwinding of DNA at the origin, and synthesis of new strands, forms a replication fork.

Chemical interaction of these nucleotides forms phosphodiester linkages, creating the phosphate-deoxyribose backbone of the DNA double helix with the bases pointing inward.

DNA polymerases are a family of enzymes that carry out all forms of DNA replication.

Initiator proteins recruit other proteins and form the pre-replication complex, which separate the DNA strands at the origin and forms a bubble.

All cellular life forms and many DNA viruses, phages and plasmids use a primase to synthesize a short RNA primer with a free 3 ′ OH group which is subsequently elongated by a DNA polymerase.

Typically, to generate the name of an enzyme, the suffix-ase is added to the name of its substrate ( e. g., lactase is the enzyme that cleaves lactose ) or the type of reaction ( e. g., DNA polymerase forms DNA polymers ).

In prokaryotes, most of the genome ( 85-90 %) is non-repetitive DNA, which means coding DNA mainly forms it, while non-coding regions only take a small part.

Other forms involve directly correcting a mutation, or using DNA that encodes a therapeutic protein drug ( rather than a natural human gene ) to provide treatment.

If the DNA sequence at a particular locus varies between individuals, the different forms of this sequence are called alleles.

DNA and many polypeptides can also form LC phases and this too forms an important part of current academic research.

Along with RNA and proteins, DNA is one of the three major macromolecules that are essential for all known forms of life.

Current fossil and DNA evidence shows that all existing species can trace a continual ancestry back to the first primitive life forms.

Nitrogen fixation, natural and synthetic, is essential for all forms of life because nitrogen is required to biosynthesize basic building blocks of plants, animals and other life forms, e. g., nucleotides for DNA and RNA and amino acids for proteins.