Satellite DNA is the chief component of chromosomal centromeres, which hold two sister chromatids together. Satellite DNA nucleotide bases occur at different ratios than the nucleotide bases of normal DNA, which makes satellite DNA denser than regular DNA. Satellite DNA is so named because when DNA is separated according to its density, the satellite DNA makes a large ring around the rest of the DNA.
Satellite DNA is non-coding. Unlike coding DNA, it does not instruct the cells to manufacture proteins. Additionally, satellite DNA is a repeating sequence of code. Some of this repetition consists of a single repeating nucleotide base, but other examples may repeat long pieces of code based on dozens of nucleotides. In addition to forming the centromeres, satellite DNA is also found in other portions of the chromosomes, but it is most common near the centromeres.
Scientists do not fully understand satellite DNA. Some satellite DNA has been demonstrated to code for the production of RNA rather than proteins. Because its purpose is not fully understood, this repeating, non-coding DNA is often called “junk DNA.”
Satellite DNA is restricted to eukaryotic organisms. Forensic scientists “fingerprint” DNA samples by recording the pattern by which the repeating satellite DNA segments differ.