Question

From this question (How pitch of a DNA Helix is 3.4 nm?), I've learnt that for counting the number of axial rise for 10 base pairs in 1 helical turn to measure the pitch of B-DNA, we have to include the space above1st base pair and below 10thbase pair as per this image - But now I'm confused as to why we include these spaces. Why do calculations fail if we were to measure starting from the base-pairs itself?

Answer 1

The pitch of a DNA helix is 3.4 nm because it represents the distance of one complete turn of the helix, including the spaces above the 1st base pair and below the 10th base pair is necessary because it accounts for the full distance covered in one complete turn of the helix.

Step-by-step explanation:

The pitch of a DNA helix is 3.4 nm because it represents the distance of one complete turn of the helix. The number of base pairs per turn is determined by the spacing between the nucleotides. Including the spaces above the 1st base pair and below the 10th base pair in the measurement of the pitch is necessary because it accounts for the full distance covered in one complete turn of the helix.