Question

What is the full turn of a DNA helix?

Answer 1

Hint: Deoxyribonucleic acid (DNA) is a polymer of nucleotides which forms polynucleotide chains that coil around each other to create a double helix and carry genetic instructions for all known organisms and viruses' formation, function, growth, and reproduction. There are various forms of DNA but the most common form of DNA found in the human body is the B-DNA.

Complete answer:
It is known that the B form, as defined by Watson and Crick, predominates in cells.
In B form of DNA the breadth is 23.7 Angstrom per 10bp of sequence, and it extends 34 Angstrom every 10bp of sequence.
Therefore, In solution, the double helix rotates one full revolution in its axis every 10.4- 10.5 base pairs.
The stacking pressures imposed by each base on its surrounding bases in the chain have a significant impact on its helical pitch.

Additional information:
At a distance of 3.4nm, the double helix DNA produces one full turn. Each full turn of DNA consists of 10 base pairs. Pitch is the term for the distance covered by a DNA molecule in one full turn. Helical pitch is the vertical distance between two locations on a helix after one complete "turn" (relative to the helical axis). The two adjacent base pairs in a DNA molecule are separated by 0.34nm.

Note:
The above question can be answered alternatively as follows:
The structure of B DNA is a right handed helix with major and minor grooves in it. DNA is 20 Angstrom in diameter. In a single round, there are 10 base pairs and the distance between them is 3.4 Angstrom. So 10 X 3.4= 34 Angstrom is the entire length of one DNA turn.