How many base pairs are there in one complete turn of the DNA helix?

1. Each base pair is separated from the next by 0.34 nanometres. 2. Each turn of the helix measures 3.4 nanometres. 3. Dividing 3.4 by 0.34 gives ten. 4. Therefore, ten base pairs are present per turn of the helix. 5. This regular geometry is what made the X-ray diffraction pattern readable. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 14 'DNA Structure and Function', sections 14.1-14.6_