Alternative Forms of DNA

Alternative Forms of DNA

A-DNA, B-DNA, and Z-DNA

• A-DNA:
  • Right-handed double helix
  • Wider and shorter than B-DNA
  • Found in dehydrated DNA or in the presence of certain ions
• B-DNA:
  • Right-handed double helix
  • Most common form of DNA in nature
  • 10 base pairs per turn, pitch of 34 Å
• Z-DNA:
  • Left-handed double helix
  • Found in regions with high GC content
  • 12 base pairs per turn, pitch of 45 Å

Triplex DNA

• Formed when a third strand of DNA binds to a double helix
• Can be parallel or antiparallel to the target DNA
• Stabilized by Hoogsteen or reverse Hoogsteen bonds
• Plays a role in gene regulation and DNA repair

G-quadruplex DNA

• Formed when four guanine bases come together
• Stabilized by hydrogen bonding and π-π stacking
• Found in telomeres, gene promoters, and untranslated regions
• Implicated in gene regulation, DNA repair, and cancer

Cisplatin-DNA Adducts

• Formed when cisplatin binds to DNA
• Causes intrastrand crosslinks and bending of the DNA
• Leads to inhibition of DNA replication and transcription
• Used as a chemotherapeutic agent in cancer treatment

I-Motif DNA

• Formed when cytosine-rich sequences come together
• Stabilized by hemiprotonated cytosine-cytosine+ pairs
• Found in promoter regions and plays a role in gene regulation
• Implicated in cancer and neurological disorders