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Unformatted text preview: teps of 3.4 Å. http://osulibrary.oregonstate.edu/specialcollections/coll/pauling/dna/pictures/franklin-typeBphoto.html H-bonds between Watson-Crick base pairs provide specificity in the
double helix but most of the stability comes from base stacking
H O N C C N NH
N NH N A C O N
CC C C C N G and C form
three H-bonds O H
NH N H N C
H H H
C C C G HN C C
H O A forms two Hbonds with T or U C-H HN
N T Base-pairing explains Chargaff’s rules for the base composition of DNA: A = T; G = C
“It has not escaped our notice that the specific pairing we have postulated
immediately suggests a possible copying mechanism for the genetic
material.” -- J.D. Watson & F.H.C. Crick, Nature 171: 737 (1953) The B-form DNA helix has a diameter of about 20 Å ~20 Å Base
Base pairs fill the center of the helix; the phosphates are on the outside.
A base pair is more exposed to the solvent on one side (the “major groove”,
at the top in these views) than the other (the “minor groove”, bottom). B-form DNA consists of a right-handed double helix with antiparallel strands
3.4 Å per
base-pair 5’ 3’ minor major groove
34 Å (10 bp)
groove minor groove 3’ 5’ These dimensions are for DNA fiber...
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- Fall '10