Secondary structure of DNA Flashcards
Chargaff’s rule
the % of A = T and G = C
Rosalind Franklin
used X-ray crystallography to identify the secondary structure of DNA
- took the famous photo 51that showed DNA molecules are helical and had 2 periodicities along the axis, a primary one of 3.4Å and a secondary one of 34Å
Francis Crick and James Watson
came up with a model for DNA secondary structure
Double helix geometry
- 2 strands wind around a single axis forming a right-handed double helix
- hydrophilic sugar-phosphate backbone is on the outside
- hydrophobic bases are stacked inside perpendicular to the helix axis
- 2 strands of DNA are antiparallel: 3’,5’-phosphodiester bonds run in opposite directions
- diameter of the double helix is 20Å
self complementarity
allows each pre-existing strand of double helix to serve as a template for DNA synthesis
- explained reproduction and damage repair
Watson-Crick base pairs
- 3 H-bonds hold G and C together
- 2 H-bonds hold A and T together
The more G and C the harder to separate the 2 DNA strands
Supercoiling
- gives DNA very compact structures
- strands of DNA cannot be separated except by unwinding from an end
Major and Minor grooves
the glycosidic bond of a base pair is not collinear - it’s at an angle
Major groove: large angle
Minor groove: short angle
- minor and major grooves alternate on the surface of the double helix
- each groove is lined by potential hydrogen bond donor and acceptors
- the larger the size of the major groove, the more accessible for interactions with proteins that recognize specific DNA sequences
What forces stabilize the double helix
- Hydrophobic effect (hydrophobic bases are hidden at the core)
- H-bonding of base pairs
- van der Waals stacking of bases
the central dogma
DNA is transcripts to RNA is translated to protein
