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?

Verified step by step guidance

1. Examine the structural features of B-DNA and Z-DNA. B-DNA is a right-handed helix, characterized by a smooth backbone and consistent major and minor grooves. Z-DNA is a left-handed helix, with a zigzag backbone and alternating purine-pyrimidine sequences.
2. Identify the handedness of a helix by observing the direction of the twist. A right-handed helix twists clockwise when viewed from the top, while a left-handed helix twists counterclockwise.
3. Analyze structure (a) and determine the direction of its twist. Look for characteristics such as the smooth or zigzag backbone and the orientation of the grooves to infer whether it is B-DNA or Z-DNA.
4. Analyze structure (b) using the same criteria. Observe the twist direction and structural features to determine whether it is right-handed or left-handed.
5. Compare the findings for structures (a) and (b) to conclude which one is right-handed and which one is left-handed, based on the observed characteristics and the definitions of B-DNA and Z-DNA.

Key Concepts

B-DNA and Z-DNA Structures

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.

Right-Handed vs. Left-Handed Helices

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 and Analysis

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.