Q.Collect information about B and Z forms of DNA. Sketch the diagrams and write the differences between these two forms.

B-DNA is the common right-handed Watson-Crick double helix found in cells, while Z-DNA is a rarer left-handed form with a zigzag sugar-phosphate backbone that forms in stretches of alternating purine-pyrimidine bases (such as GCGCGC), especially under high salt. Sketch both as double helices, one turning right and one left, and tabulate their differences in handedness, backbone shape, base pairs per turn, pitch, diameter and grooves. …

Aim. To collect information on the B and Z forms of DNA, sketch them and tabulate their differences.

Background. The Watson-Crick model describes the B form, the double helix present in cells under normal conditions. DNA can also adopt other conformations; the Z form (Rich and co-workers, 1979) is a left-handed helix whose backbone zigzags, seen in sequences of alternating purines and pyrimidines such as GCGCGC under high salt concentration or in negatively supercoiled DNA. (The A form is a third, wider right-handed form seen in dehydrated DNA; it is not part of this project.)

Sketches to draw. 1. B-DNA: a right-handed double helix, the two sugar-phosphate backbones as ribbons twisting clockwise upward, base pairs as horizontal rungs, with a wide major groove and a narrow minor groove marked. 2. Z-DNA: a slimmer left-handed helix, the backbones drawn as zigzag lines twisting anticlockwise upward, with its single deep narrow groove marked. Label the diameter, the pitch (length of one turn) and the number of base pairs per turn on each.

Differences to tabulate.