DNA ladder
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A DNA ladder is a solution of DNA molecules of different lengths used in agarose gel electrophoresis. It is applied to an agarose gel as a reference to estimate the size of unknown DNA molecules. In addition it can be used to approximate the mass of a band by comparison to a special mass ladder.
The DNA ladder is made of 4 different nucleotides which link the 2 sides of the strand. They are called: adenine "A", thymine "T", Cytosine "C" and last Guanine "G."
Different DNA ladders are commercially available depending on expected DNA length. The 1kb ladder with fragment ranging from about 0.5 kbp to 10 or 12 kbp and the 100 bp ladder with fragments ranging from 100 bp to just above 1000 bp are the most frequent. DNA ladders are often produced by a suitable restriction digest of a plasmid. There are special DNA ladders for supercoiled DNA and RNA.
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