Final answer:
B DNA is a right-handed helix and occurs under normal physiological conditions in living organisms. A DNA is also a helix, but left-handed, and is found in specific situations. Z DNA is a triple helix and forms under specific DNA sequence conditions.
Step-by-step explanation:
Regarding the conformational characteristics of different forms of DNA, the correct description is:
B DNA - Right-handed helix
A DNA - Right-handed helix, but with a more compact and less hydrated form than B-DNA
Z DNA - Left-handed helix
Triple-helical DNA is a less common form, and it is not one of the options listed in A, B, C, or D. Therefore, the correct option describing when these forms of DNA occur is C) B DNA - Right-handed helix; A DNA - Double helix; Z DNA - Left-handed helix.
Conformational Features:
B DNA: It is the most common form of DNA in living cells and is characterized by a right-handed double helix. Its helical structure presents major and minor grooves where proteins may bind to regulate genetic processes.
A DNA: This right-handed helical form is similar in appearance to B DNA but differs in its geometry, often found in dehydrated DNA samples and rarely in functional cells.
Z DNA: This form has a left-handed helical structure and Z-shaped zigzag backbone. It occurs transiently in cells, possibly during certain biological processes like transcription.
The three forms are stabilized by hydrogen bonds between nitrogenous bases and the sugar-phosphate backbone forms the exterior part of the helix. They are important for DNA's role in storing and transferring genetic material.