Comparison of different helical parameters of A, B, and Z – DNA

A – DNA

  • Much wider and flatter.
  • Right handed helix.
  • major grooves: Narrow and deep
  • minor grooves: wide and shallow
  • Glycosidic bonds – anti-form
  • 11 base pair

B – DNA

  • Solid central core.
  • Right handed
  • Major groove: wide and narrow
  • Minor groove: narrow and deep
  • Glycosidic bond – anti-form
  • 10 base pair

Z – DNA

  • Solid core at centre.
  • Left handed
  • Major groove: More or less flat
  • Minor groove: narrow and deep
  • Glycosidic bond  is anti-for Pyrimidines and syn-for Purines
  • 12 base pairs
Different forms of DNA- A form, B form, Z form | Molecular Biology |  Microbe Notes
ParameterA-DNAB-DNAZ-DNA
Helix senseRightRightLeft
Base pairs per turn111012
Axial rise0.260.340.45
Helix pitch28344.5
Base pair tilt20-67
Twist angle3336-30
Diameter of helix2.32.01.8