Question

Which DNA among the following is left-handed?
A. Z-DNA
B. A-DNA
C. C-DNA
D. B-DNA

Answer 1

Hint: DNA is a molecule composed of two polynucleotide chains that coil around one another to create a double helix carrying genetic instructions for the development, functioning, growth, and reproduction of all known organisms. DNA and ribonucleic acid (RNA) are nucleic acids.

Complete answer:
Looking at the options the first option is Z-DNA. Z -DNA is one of the possible double helical structures of DNA. It is a left-handed double helical structure where the double helix winds to the left in a zig-zag manner.
The second option is the A-DNA. It is a right-handed double spiral which is similar to the B-DNA form. Dehydrated DNA needs an A form that protects DNA throughout extreme conditions such as desiccation. The third option is C-DNA. It is Complementary DNA and it is single-stranded.
The fourth option is the B-DNA. This is the most common form of DNA conformation and it is a right-handed spiral. The majority of DNA has a B type conformation under normal physiological situations. So the only left-handed DNS is Z-DNA
Hence, the right answer is Option A (Z-DNA)

Additional Information:-
Sequences that can form Z-DNA are generally not found in Escherichia coli, but however, they are overrepresented in complex eukaryotes. A notable example of this is the CpG islands, which could potentially form Z-DNA, especially when methylated. Besides, Z-DNA has also been functioned to play the role of a transcription enhancer, and also in differentiating terminals. In some eukaryotic genomes, ten percent or more of the genome contains sequences capable of forming Z-DNA.

Note: Whether a DNA sequence will be in the A, B, or Z-DNA conformation depends on at least three conditions. The first condition is the hydration environment, which facilitates conversion between different helical forms. The second condition is the DNA sequence. The third condition is the presence of proteins that can bind to DNA in one helical conformation and which forces the DNA to adopt a different conformation.