Final answer:
DNA is packaged into a structure called a chromosome inside cells. In prokaryotes, supercoiling helps in this process, while in eukaryotes, DNA wraps around histone proteins to form nucleosomes and further condenses into chromatin fibers, ultimately forming chromosomes.
Step-by-step explanation:
When the DNA molecule folds, coils, and supercoils to fit inside a cell, it forms a structure known as a chromosome. In prokaryotic cells, like E. coli, DNA supercoiling helps to fit the large DNA molecule into a very small space. In eukaryotic cells, the process is more complex, involving the winding of DNA around histone proteins to form nucleosomes, which look like 'beads on a string.' These nucleosomes further coil into a 30-nm chromatin fiber. During cell division, the chromatin fibers condense even further to form the tightly-packed chromosomes visible under a microscope.
The degree of DNA supercoiling can vary, resulting in DNA that is either under-wound or over-wound. Proteins like topoisomerases are involved in maintaining the supercoiled structure of chromosomes, which is crucial for efficient DNA replication and transcription. This intricate packaging allows DNA, which can be up to 2 meters long in humans, to fit within the tiny nucleus of a cell.