Non-B DNA Structures Quiz

Non-B DNA Structures: A-DNA, Z-DNA, Cruciform, Triplex, and Quadruplex

• A-DNA is a right-handed double helix with 11 bp per helical turn, tilted base pairs, axial hole, and deep major groove.
• B-DNA is the predominant DNA form in living systems, with 10.5 bp per helical turn, minor and major grooves of similar depths, and no axial hole.
• Z-DNA has a left-handed helix, zigzag sugar-phosphate backbone, and a single groove.
• Z-DNA can be formed by d(CG)3 or d(CA)3 at high salt concentrations, and it may exist transiently in cells and play a role in regulating gene expression.
• Cruciform structure can be formed by inverted repeat sequences, and it consists of double-stranded branches that are somewhat strained compared to normal duplexes.
• Triplex structure can be formed by a third strand in the major groove of DNA, and it can increase the likelihood of double-strand breaks and mutations.
• Quadruplex structure can be formed by one, two, or four G-rich DNA strands, and it consists of quartets stacked on one another, stabilized by hydrogen bonds and cation-dipole interactions.
• Intramolecular quadruplexes may form from the G-rich 3′-overhangs of eukaryotic chromosomes and influence chromosome replication and stability.
• Non-B DNA structures may exist transiently in cells or play a role in regulating gene expression.
• Non-B DNA structures may also be hot spots for DNA double-strand breaks and chromosomal rearrangements that result in malignant diseases.
• DNA crystals can provide information about the distances between specific base pairs, but DNA isolated from natural sources is too heterogeneous to form crystals.
• Organic chemists have developed methods for synthesizing homogenous DNA samples that can form crystals, leading to the discovery of Z-DNA and other non-B DNA structures.