Final answer:
Nucleic acids can adopt a left-handed conformation called the Z helix, which typically occurs under high ionic strength, when the DNA has a high GC content, or in sequences alternating in purines and pyrimidines.
Step-by-step explanation:
Nucleic acids, such as DNA and RNA, can adopt various structural conformations. While the B-form double helix is the most common and well-recognized structure of DNA, with its characteristic right-handed spiral and major and minor grooves, there exists another, less common form known as the Z helix. The Z helix is a left-handed conformation that DNA can sometimes adopt, under certain conditions. This structure is more zigzagged in appearance and typically occurs under high ionic strength, when the DNA has a high GC content, or in sequences alternating in purines and pyrimidines. It is not as prevalent as the B-form helix because it does not form as spontaneously; rather, it is often induced by biological activity such as transcription or the binding of certain proteins.