dsDNA Structures

Question 1

A Form

• Helical Sense:
• Diameter:
• Base Pairs/Turn:
• Helix Rise/Base Pair:
• Base Tilt to Axis:
• Pucker:
• Glycosyl Bond:

Answer 1

• Non-aqueous solution
• Most crystalline form
• Dimensions:
  
  • Helical Sense: right-handed
  • Diameter: 26 Å
  • Base Pairs/Turn: 11
  • Helix Rise/Base Pair: 2.6 Å
  • Base Tilt to Axis: 20°
  • Pucker: C-3’ endo
  • Glycosyl Bond: anti

Question 2

B Form

• Helical Sense:
• Diameter:
• Base Pairs/Turn:
• Helix Rise/Base Pair:
• Base Tilt to Axis:
• Pucker:
• Glycosyl Bond:

Answer 2

• Watson-Crick form
• Random base sequence
• Physiological conditions

Dimensions:

• Helical Sense: right-handed
• Diameter: 20 Å
• Base Pairs/Turn: 10.5
• Helix Rise/Base Pair: 3.4 Å
• Base Tilt to Axis: 6°
• Pucker: C-2’ endo
• Glycosyl Bond: anti

Question 3

Z Form

• Helical Sense:
• Diameter:
• Base Pairs/Turn:
• Helix Rise/Base Pair:
• Base Tilt to Axis:
• Pucker:
• Glycosyl Bond:

Answer 3

• Alternating C, G
• Short tracks in prokaryotes and eukaryotes

Dimensions:

• Helical Sense: left-handed
• Diameter: 18 Å
• Base Pairs/Turn: 12
• Helix Rise/Base Pair: 3.7 Å
• Base Tilt to Axis: 7º
• Pucker:
  
  • C-2’ endo for pyrimidines
  • C-3’ endo for purines
• Glycosyl Bond:
  
  • anti for pyrimidines
  • syn for purines

Question 4

Structures Compared

Answer 4