Satellite DNA

As a highly repetitive satellite DNA sequences, ie recurring several times base sequences in the genome of higher organisms ( eukaryotes ) are referred to in genetics.

Name

The term satellite DNA is due to the distinction between genome fragments of their GC content, and thus on its density by CsCl - centrifugation technique. Plotting in a graph the DNA concentration against its density, is obtained In addition to the major band (peak) several minor bands, which are also referred to as satellite peaks. The main band therefore represents the average density of DNA.

Properties

Most often it is repeated sequences of five to ten base pairs, but also can be very much longer and may extend over areas of up to 100,000 base pairs. In an average mammalian genome there are about ten percent of the DNA from these simply -structured DNA sequences. These sections have a particularly high renaturation rate.

In mammals, the majority of these ranges in heterochromatin near the centromere, Drosophila melanogaster or also at the telomeres. The microtubules of the spindle apparatus attach to the centromeres in to the mitosis and meiosis.

Demarcation

In general, we distinguish between three classes of satellite DNA.

Classical satellite DNA is between 100 and 5000 kb in length. It consists of up to a million repetitions of frequencies of a length between 5 and 300 bp, and is not transcribed in the rule. In the alpha repeats at centromeres of chromosomes classical satellite DNA has a role as a protein binding site.

Minisatellite (short tandem repeats ) are, as the name suggests, is smaller than the classical satellite DNA. They are long usually between 100 bp and 20 kb, their repeat units contain a maximum of 15 bases. At the telomeres, they act as binding sites for proteins that serve to protect from degradation by nucleases.

Microsatellite (simple sequence ) are several hundred repeats 1-6 bp sequences shortest satellite DNAs. They themselves are repetitive units, which are spread over the entire genome occur up to 100,000 times. Microsatellites are probably formed during replication, when free DNA ends are present and there is a slippage ( slippage ) of the DNA polymerase. The relatively random origin of microsatellites also attracts a large length polymorphism by itself, which is used for genetics and forensics. As the fingerprint is also the microsatellite length polymorphism, a distinguishing feature for proper identification of an individual.

Swell

• Catherine Munk, pocket textbook Biology Genetics, 2010 Georg Thieme Verlag (ISBN 978-3-13-144871-2 )
• Rolf Knippers, Molecular Genetics, 2006 Georg Thieme Verlag (ISBN 978-3-13-144871-2 )

• Repetitive DNA