Nucleotides & Nucleic Acids

Watson & Crick 1953 (Franklin & Wilkins too)

Franklin & Wilkins

X - indicates helical structure

Heavy bands - indicates recurring bases

Nucleotides & Nucleic Acids

Watson & Crick 1953 (Franklin & Wilkins too)

Watson & CrickUsed x-ray crystallography dataUsed Chargaff’s rules3D structure of DNA, strands antiparallel

Nucleotides & Nucleic Acids

DNA structureComplementarityStrands not identical in base sequence or composition

DNA replication

Nucleotides & Nucleic Acids

DNA structure - different forms

A-DNA B-DNA

Z-DNA

Nucleotides & Nucleic Acids

DNA structure - different forms

Structuretype

A

B

Z

Pitch (Å)

28.2

33.8

45

Axial rise (h) per nt (Å)

2.56

3.38

3.7

Groove width (Å)

minor major 11 2.7

5.7 11.7

8.8 2

Groove depth (Å)

minor major 2.8 13.5

7.5 8.5

3.7 13.8

axial rise (h)distance between bp

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

Z-DNA virtually no major groove due to syn-G, pulls C into major grv

purine rotatedinto major groove

A-DNA A-DNA + bulgeB-DNA

32˚

tilt

ed u

pw

ard

Triple HelixIntrastrand base pairing

Triple Helix using a third strand of DNAInterstrand base pairing

Restriction endonuclease