DNA ladder

A DNA ladder is a mixture of different strands of DNA of known length, which is used for determining the size of DNA in a sample as Komigrationsstandard in an agarose gel electrophoresis. From the known amount of the DNA in the Komigrationsstandard can next be obtained in a sample, a quantification of the DNA is estimated. Furthermore, the term DNA ladder is used for a characteristic length pattern of agarose gel electrophoresis of apoptotic cells.

A standard DNA ladder fragments includes from about 100 base pairs to 10,000 base pairs. Specific DNA ladders can have their focus in the area of particularly long or particularly short DNA fragments, thus facilitating a more accurate size determination. There are also conductors which are particularly suitable for determining the size of the RNA.

Example

In the figure on the right is an example of a DNA ladder is shown. This is a photo of a typical agarose gel (1% agarose) in UV light. The bright bands are the DNA fragments that fluoresce red by staining with ethidium bromide under UV light. In the first lane is the DNA ladder, the lateral sizes ( bp for base pairs ) of the respective fragments are indicated. The total DNA amount of the applied head is 1 ug. In the second and third trace DNA samples were separated. The first sample contains four different sized fragments of approximately 4500, 2500, 1500 and 1300 bp. The second sample contains a fragment of 8000 and one of 2500 bp. On the basis of intense bands can be seen that the first sample of DNA containing little more than the second sample.

Molar Mass

The mathematical relationship between the number of base pairs ( also approximately the molecular weight ) and the distance covered in the agarose gel is logarithmic. By a semilogarithmic plot on a graph, the correlation can be linearized.

DNA ladder associated with apoptosis

Related to programmed cell death, the DNA ladder is used as a highly sensitive indicator of apoptosis. The phenomenon was described in 1980 by Andrew H. Wyllie from the University of Edinburgh Medical School first.

Endonucleases cleave in the course of apoptosis, genomic DNA between the nucleosomes ( linker region ) while producing DNA fragments with a length of about 180 base pairs. The DNA ladder arises from the fact that the DNA is protected in the area of ​​nucleosomes from degradation by DNase, whereas the intermediate regions can be hydrolyzed. In contrast, necrosis occurs in the degradation of DNA into fragments of random size that occur in an agarose gel as a "smear". The presentation of the " Apotoseleiter " is therefore a sensitive method to apoptosis from ischemic or toxic cell death delineate.