Considering the information on B- and Z-DNA and right- and left-handed helices, carefully analyze structures (a) and (b) below and draw conclusions about their helical nature. Which is right-handed and which is left-handed?

B-DNA is the most common form of DNA in cells, characterized by a right-handed helix with about 10.5 base pairs per turn. In contrast, Z-DNA is a left-handed helix that forms under certain conditions, such as high salt concentrations or specific sequences. Understanding these structural differences is crucial for analyzing the helical nature of DNA.

The terms 'right-handed' and 'left-handed' refer to the direction in which the helix twists. Right-handed helices, like B-DNA, twist clockwise, while left-handed helices, like Z-DNA, twist counterclockwise. This distinction affects the physical properties and biological functions of the DNA.

Helical parameters, such as pitch, rise per base pair, and base pair orientation, are essential for determining the handedness of a DNA structure. By analyzing these parameters in the provided structures, one can conclude whether they exhibit right-handed or left-handed helical characteristics, which is vital for understanding their biological roles.