1. Nucleotides & Nucleic Acids
Watson & Crick (Franklin & Wilkins too)
Franklin & Wilkins
Heavy bands - indicates recurring bases
X - indicates helical structure

2. Nucleotides & Nucleic Acids
Watson & Crick (Franklin & Wilkins too)
Watson & Crick
Used x-ray crystallography data
Used Chargaff’s rules
3D structure of DNA, strands antiparallel

3. Nucleotides & Nucleic Acids
DNA structure
Complementarity
Strands not identical in base sequence or composition
DNA replication

4. Nucleotides & Nucleic Acids
DNA structure - different forms

5. A-DNA
B-DNA
Z-DNA

6. Nucleotides & Nucleic Acids
DNA structure - different forms
Structure
type A B Z
Axial rise (h)
per nt (Å)
2.56
3.38
3.7
Groove width
(Å)
minor major
Groove depth
(Å)
minor major
Pitch (Å)
28.2
33.8 45
Z-DNA virtually no major groove due to syn-G, pulls C into major grv
Pitch = axial rise x repeat (bp/turn)
distance for complete turn of helix
So for A-DNA  2.56 Å x 11 bp/turn = 28.2 Å
axial rise (h)
distance between bp

8. purine rotated
into major groove

9. A-DNA
B-DNA
A-DNA + bulge
32˚ tilted upward

19. Intrastrand base pairing
Triple Helix
Intrastrand base pairing

21. Triple Helix using a third strand of DNA Interstrand base pairing
Restriction endonuclease