What is the distance between adjacent base pairs in B-DNA in angstroms? The distance is approximately 3.4 Å.
This measurement is called the rise per base pair: the average distance along the helix axis from one stacked base pair to the next. It equals 0.34 nanometres, or 3.4 × 10⁻¹⁰ metres. The value is a defining geometric feature of the common B-DNA form.
B-DNA makes roughly one complete turn every 10 base pairs. Multiplying about 10 base pairs by 3.4 Å gives a helical pitch of approximately 34 Å, or 3.4 nm. The bases are stacked inside the helix, while the negatively charged phosphate groups form the outer sugar-phosphate backbones.
The number is often confused with DNA’s diameter, which is about 20 Å, or with the spacing in other DNA conformations. A-DNA has a shorter rise of roughly 2.6 Å, while Z-DNA has a rise of about 3.7 Å, so the 3.4 Å figure specifically identifies the standard B-form geometry.