Which of the following descriptions about the different forms of DNA is not correct?

a. A-DNA has a deeper major groove then B-DNA

b. There are 10.5 base pairs per helical turn in B-DNA

c. Z-DNA is a zigzag left-handed helix

d. Z-DNA is favored in sequences with long repeats of purines alternating in the syn - and anti-conformation.

e. A-DNA is favored in solutions relatively devoid of water.

Option (d).

Explanation:

DNA is the genetic material of the living organisms (except few viruses). Three different forms of DNA are A-DNA, B-DNA and Z-DNA. B form of DNA is more common and stable form of DNA.

Z-DNA has the ability to form in the junctions between the B-DNA. The Z DNA has both syn and anti conformation favored by the long repeats of the alternating purines and pyrimidine sequences. Only the pyrimidine sequences are not favorable for the Z-DNA structure.

Thus, the correct answer is option (d).