In the field of biology, nick translation is a process used to replace certain molecules that make up strands of DNA with similar molecules that produce a specific, desired characteristic, often a characteristic that allows these molecules to be easily spotted and identified during an experiment. An enzyme known as DNA Polymerase I causes certain DNA molecules, known as nucleotides, to be replaced with new nucleotides. The new nucleotides are picked specifically by the scientists performing the experiment.
Often nick translation is used for scientific procedures such as blotting. This involves isolating and examining strains of DNA to determine what nucleotides it consists of and then performing experiments on the particular strand of DNA. Learning about different DNA sequences can help isolate a mutation or create an antibody to fight off a virus.
The process of nick translation involves what are referred to as restriction enzymes used to make cuts or "nicks" on the DNA sequence. A restriction enzyme is designed to cut a DNA sequence in a specific location and is a type of defense mechanism used to destroy harmful viruses. Scientists put the restriction enzyme to work cutting pieces of the DNA so they can replace them with new pieces.
Once the nicks are made, specific enzymes are used to repair the DNA with special nucleotides designed to make studying the DNA easier. Scientists study this new DNA sequence to see how it reacts to itself or other objects, and having these tagged nucleotides simplifies the process of closely monitoring and studying the DNA strand. A common example is the insertion of tagged nucleotides which will glow when placed under a black light, thus making them easy to spot.
Another common example of one of the many uses of nick translation is fluorescent in situ hybridization. This process allows a scientist to look for specific DNA sequences to see whether or not they are present in a strand of DNA. Nick translation can give these strands of DNA fluorescent properties so they glow and the scientist can use this to help identify which DNA sequences are present and which are absent.
Nucleotides removed and then replaced through nick translation are often termed "junk DNA." Scientists have not yet been able to find any sort of purpose that these DNA molecules serve. They appear to be non-functioning and do not carry the code for any sort of protein, as is typical of most useful DNA.