Final answer:
Mammalian DNA is densely packed within the cell nucleus through a process called supercoiling, facilitated by proteins and enzymes that maintain the structure of supercoiled chromosomes.
Step-by-step explanation:
Mammalian DNA is incredibly long and must be tightly packaged within the confines of the cell nucleus. This packaging of DNA is necessary as the DNA does not exit the cell's nucleus during its lifecycle.
In humans, if the DNA from all 46 chromosomes were laid out end to end, it would measure up to two meters in length, while its diameter would be only 2 nm. To accommodate this discrepancy, DNA undergoes supercoiling, a process where it is twisted into more compact forms.
Supercoiling can cause DNA to be under-wound or over-wound from its normal state.
Furthermore, specific proteins like topoisomerases and enzymes such as DNA gyrase are involved in maintaining the structure of supercoiled chromosomes, especially during DNA replication and other cellular processes that require the DNA to be manipulated.