What allows DNA to fit inside the nucleus of a cell?

DNA fits inside the nucleus of a cell primarily because it coils tightly around associated proteins, which are known as histones. This coiling and packaging process forms structures called nucleosomes, where DNA wraps around histone proteins, creating a bead-like structure. These nucleosomes further coil and fold into a more compact structure called chromatin. This highly organized packing mechanism allows the large length of DNA, which if stretched out would be several meters long, to fit within the relatively tiny nucleus of a cell, which is only about 10-30 micrometers in diameter.

The other choices do not adequately describe the compacting mechanism of DNA. It is not RNA that is involved in this process but rather a specific arrangement of proteins (histones). While DNA does indeed form double strands, this structural feature pertains more to its stability and replication rather than its ability to fit within the nucleus. Breaking DNA down into smaller sequences does not facilitate packing; rather, it would defeat the purpose of storing the genetic information in a cellular context.