Final answer:
There are approximately 10.5 base pairs per turn in the double helical structure of DNA under physiological conditions.
Step-by-step explanation:
In the double helical structure of DNA, one full turn of the helix traditionally consists of approximately 10 base pairs, according to Watson and Crick's model, where they used Rosalind Franklin and Maurice Wilkins' X-ray crystallography data.
However, more recent data suggest that there are 10.5 base pairs per turn under physiological conditions, with each base pair being separated by a distance of 0.34 nm. This slight adjustment accounts for the most stable structure of DNA in the environment of a living cell.
It is important to note that each base pair consists of a purine (Adenine or Guanosine) and a pyrimidine (Thymine or Cytosine). This pairing ensures the uniform diameter of the DNA molecule at 2 nm, essential for its stable structure and function.
The twisting arrangement of the two DNA strands creates patterns of major and minor grooves, which are critical for the interaction of DNA with various proteins, such as those involved in replication, transcription, and other cellular processes.
The structure forms major and minor grooves, allowing protein interactions and ensuring DNA's stable and functional form.