Question

One of the following nucleic acids has a left handed helix:

• A. m-RNA
• B. t-RNA
• C. A-DNA
• D. Z-DNA

Hint:

Z-DNA is a left-handed helix, while most naturally occurring DNA exists in the right-handed B-DNA form.

Answer 1

The Correct Option is D

Step 1: Understanding the different forms of DNA.
DNA can exist in several forms, including A-DNA, B-DNA, and Z-DNA. Z-DNA is a left-handed helix, unlike the more common B-DNA which is right-handed.
Step 2: Analyzing the options.
(1) m-RNA: mRNA is a single-stranded RNA molecule and does not exhibit a left-handed helix structure.
(2) t-RNA: tRNA also has a distinct three-dimensional structure but does not form a left-handed helix.
(3) A-DNA: A-DNA is a right-handed helix.
(4) Z-DNA: Correct — Z-DNA is a left-handed helix, characterized by its zig-zag backbone structure.
Step 3: Conclusion.
The correct answer is (4) Z-DNA, as it is the left-handed form of DNA.