LIFE SCIENCE

Detailed explanation-1: -This is called A-form nucleic acid. A third form of duplex DNA has a strikingly different, left-handed helical structure. This Z DNA is formed by stretches of alternating purines and pyrimidines, e.g. GCGCGC, especially in negatively supercoiled DNA. A small amount of the DNA in a cell exists in the Z form.

Detailed explanation-2: -Z-DNA is a left-handed helical form of DNA in which the double helix winds to the left in a zigzag pattern. DNA containing alternating purine and pyrimidine repeat tracts have the potential to adopt this non-B structure in vivo under physiological conditions, particularly in actively transcribed regions of the genome.

Detailed explanation-3: -Z-DNA is a higher-order structure known to form in alternating purine-pyrimidine or pyrimidine-purine (APP) dinucleotide repeat sequences, with the propensity of Z-DNA to form in the order GC>CA>TA (Ellison et al.

Detailed explanation-4: -Another Z-DNA-binding protein is E3L, which is found in poxviruses, including the vaccinia virus. These large DNA viruses reside in the cytoplasm of cells and produce several proteins that help to abort the interferon response of the host cell.

Detailed explanation-5: -Unlike the A and B forms, Z-DNA is a left-handed double helical structure with 12 base pairs per turn.