Each chromosome in the cell nucleus contains DNA compressed to over 10,000 times shorter than it would be if it were to be stretched out. Despite this compression, each chromosome is capable of rapidly unwinding, taking up new complementary nucleotides and reforming during each cycle of mitosis.
The key to the chromosome's extraordinary DNA compression is in its unique folding pattern. Within each chromosome, the DNA double helix is twisted into a spiral, then twisted again to make the greatest possible use of the minute volume available to it. This multiple-twisting mechanism permits a sequence of billions of nucleotides to be contained within just 46 chromosomes for humans.