What is the difference between A, B and Z forms of DNA?
Following are the differences between A, B and Z forms of DNA -:
| Criteria | A-DNA | B-DNA | Z-DNA |
| Helix Type | Right-handed helix | Right-handed helix | Left-handed helix |
| Helix Diameter | 23 Å (Angstroms) | 20 Å | 18 Å |
| Base Pairs per Turn | 11 base pairs | 10.5 base pairs | 12 base pairs |
| Helical Twist | 32.7° per base pair | 36° per base pair | 9° per base pair |
| Pitch (Height per Turn) | 28.2 Å | 34 Å | 45.6 Å |
| Major groove | Narrow and deep | Wide and deep | Flat |
| Minor groove | Wide and shallow | Narrow and deep | Narrow and deep |
| Sugar Conformation | C3′-endo | C2′-endo | C2′-endo (Purines), C3′-endo (Pyrimidines) |
| Occurrence | Found in dehydrated DNA (in vitro) | Most common form under physiological conditions | Found in regions with alternating purine-pyrimidine sequences (e.g., CG repeats) |
| Stability | Less stable (occurs in low humidity) | Most stable and prevalent form | Less stable and transient |
| Biological Role | Not common in vivo, possibly in RNA-DNA hybrids or DNA during replication | Dominant form in cells | May play a role in gene regulation and DNA recombination |