Which form of supercoiling is less common in the majority of DNA?

Over-positive supercoiling is less common in most DNA molecules, particularly in bacterial and eukaryotic genomes. Supercoiling refers to the coiling of the DNA double helix, which can occur in different forms depending on the torsional strain present in the DNA molecule.

Negative supercoiling is quite common and serves important biological functions. It facilitates the unwinding of DNA, which is crucial during processes such as DNA replication and transcription. This negative supercoiling creates a state that allows for the easier separation of the DNA strands, making the genetic material more accessible for enzymatic actions.

On the other hand, over-positive supercoiling, which occurs when the DNA is twisted in the direction of the helix, leads to increased torsional strain that can hinder these essential processes. While it can happen in regions of active transcription or replication, its occurrence is not typical throughout the genome and often results from specific cellular conditions.

In summary, the prevalence of negative supercoiling compared to over-positive supercoiling is rooted in the functional requirements of DNA during cellular activities, making over-positive supercoiling the less common form found in the majority of DNA.