Define satellite DNA. Describe where it is found in the genome of eukaryotes and its role as part of chromosomes.

Satellite DNA is a non-coding, highly repetitive DNA sequence found in the genome of eukaryotes. It is composed of tandem repeats, which are short DNA sequences repeated many times in a row. These sequences are not transcribed into RNA or translated into proteins and have long been considered "junk" DNA due to their unknown functions, however, recent research has indicated that they may have essential roles in the genome organization and function.

In eukaryotic genomes, satellite DNA is primarily found in the centromeres and telomeres of chromosomes. Centromeres are the constricted regions of chromosomes where sister chromatids are held together and serve as attachment points for spindle fibers during cell division. Telomeres are the protective caps at the ends of linear chromosomes, preventing the loss of genetic information during replication and ensuring chromosome stability.

Satellite DNA has several known roles as part of chromosomes: 1. Structural role: Satellite DNA forms the structural basis of centromeres, facilitating the assembly of kinetochores, protein complexes that attach to spindle fibers during cell division. This helps ensure proper chromosome segregation and prevents chromosomal abnormalities. 2. Chromosome stability: The highly repetitive nature of satellite DNA in telomeres protects the ends of chromosomes from degradation and fusion. In each cell division, a small portion of telomeric DNA is lost, and the presence of satellite DNA ensures that essential coding DNA is not lost. 3. Epigenetic regulation: Satellite DNA can serve as binding sites for proteins that are involved in the organization of chromatin structure. This can contribute to the epigenetic regulation of gene expression. 4. Genome organization: Satellite DNA contributes to the formation of chromosomal domains and nuclear architecture, possibly influencing the spatial distribution of genes and their accessibility to transcription factors. In summary, while satellite DNA was once considered non-functional "junk" DNA, it has now been shown to play essential roles in maintaining chromosome stability, structure, and organization in eukaryotic genomes.