**DNA Structure Variants**As a result of the rotation about six of its bonds, DNA can exist in a variety of forms. Determine whether each of the images and properties represents or describes the A form, B form, or Z form of DNA.---**A Form DNA:****Properties:**- Favored form of dehydrated DNA**B Form DNA:****Properties:**- Approx. 20 Å helix diameter- Antiparallel strands- Most stable form under physiological conditions- Major groove is wide and deep- Helix image depicting the typical double helix structure**Z Form DNA:****Properties:**- Approx. 18 Å helix diameter- Left-handed**All Forms Common Characteristics:****Properties:**- Antiparallel strands (common to all right-handed DNA forms)**Diagrams:**1. **Helical Structure Diagrams:** - Illustrates the classic double helix representation, showing antiparallel strands.2. **Chemical Structure:** - Depicts nucleotide chemical details, such as the sugar-phosphate backbone. 3. **Molecular Representation:** - Shows molecular details, including the helix diameter and orientation characteristics (left-handed for Z form).This exercise helps in understanding the different structural forms of DNA and their biological significance.

There are 3 major DNA variants. They are A-DNA, B-DNA and Z-DNA. In all these variants, A pairs with T and G pairs with C. Also, the 2 strands of DNA are antiparallel to each other in all these 3 variants. In all variants, the pyrimidine nucleotides (cytosine and thymine) are in anti conformation.The deoxycytidine nucleoside given in question is in anti conformation because the nitrogenous base (i.e. cytosine; highlighted in GREEN) is towards the right (indicated by RED arrow) of the N-glycosyl bond (highlighted in YELLOW). In syn confromation the nitrogenous base is oriented towards the left of N-glycosyl bond.The variants differ from each other in other characteristics.A-DNA is the favored form of dehydrated DNA. It has the widest helix diameter among the 3 variants, that is approximately 26 A0. In A-DNA the base pairs are tilted 200 with respect to the helix axis. This 200 tilt is what we see in the DNA figure below. See how the grey lines (i.e. base pairs) are titled or slanted. Due to the 26 A0 helix diameter and the 200 tilt of the base pairs, the major groove is wide and deep in A-DNA. The helix axis is represented by the yellow line.This is the form of DNA that predominates under physiological conditions. It is a right handed helix.The base tilt normal to the helix axis is just 60 in B-DNA. For A-DNA and Z-DNA it is 200 and 70 respectively. So, the base pairs are the most perpendicular compared to the plane of helix axis in B-DNA. This is what we see in the DNA figure below. See how the grey lines (i.e. base pairs) are almost perpendicular to the helix axis. The helix axis is represented by the yellow line.The helix diameter in B-DNA is 20 A0.It is left handed and has the narrowest helix diameter of around 18 A0.The deoxyadenosine nucleoside given in question is in syn conformation because the nitrogenous base (i.e. Adenine; highlighted in GREEN) is towards the left (indicated by RED arrow) of the N-glycosyl bond (highlighted in YELLOW). In anti confromation the nitrogenous base is oriented towards the right of N-glycosyl bond.Adenine is a purine. Purines exist in syn conformation in Z-DNA. Purines exist in anti conformation in A and B-DNA.