Final answer:
DNA molecules that differ based on supercoiling are known as topoisomers. Supercoiling compacts DNA into a cell nucleus and varies between being under-wound or over-wound, which is crucial for DNA replication and transcription.
Step-by-step explanation:
DNA molecules that differ in the extent and nature of their supercoiling are referred to as topoisomers. This difference arises because supercoiling is a way that DNA becomes more compact, fitting inside the confines of a cell nucleus or bacterial cell. DNA is either under-wound or over-wound from its normal relaxed state, leading to these variations in structure, which are essential for processes like replication and transcription. In prokaryotes, DNA supercoiling is facilitated by proteins and enzymes such as DNA gyrase, while in eukaryotes, DNA is compacted by wrapping around histone proteins to form nucleosomes, further coiled into chromatin and during cell division into highly condensed chromosomes. The process involves different proteins in prokaryotes and histones in eukaryotes.