Final answer:
Z-DNA is characterized by its left-handed double helix, a zigzag sugar-phosphate backbone, a helical turn with 12 base pairs, altered hydrogen bonding patterns due to base flipping, and less pronounced major and minor grooves. These structural features distinguish Z-DNA from the right-handed B-DNA, and they affect how DNA binding proteins interact with the molecule during transcription and replication.
Step-by-step explanation:
Main Structural Features of Z-DNA
The main structural features of DNA found in the Z conformation are notably different from the more common B-DNA form. Z-DNA is a left-handed double helix, whereas B-DNA is right-handed. One distinguishing feature of Z-DNA is that it has a zigzag sugar-phosphate backbone, which gives rise to a more slender and elongated helical structure compared to B-DNA.
In Z-DNA, the helical twist is more extended with 12 base pairs per turn of the helix, unlike the 10.5 in B-DNA. Due to this alteration, the major and minor grooves are not as pronounced as they are in B-DNA. Z-DNA also features alternating purine and pyrimidine sequences, which contribute to the zigzag backbone structure.
Another distinction is the hydrogen bonding between base pairs. While hydrogen bonds are also present in B-DNA, stabilizing the complementary base pairs (A with T and G with C), in Z-DNA, the pattern of hydrogen bonding is altered due to the flip of the purine bases. This flip changes the overall topology of the DNA molecule and is one reason why Z-DNA can provide specific binding sites for DNA binding proteins during processes such as transcription and DNA replication, albeit in a different manner from B-DNA.