Nucleic Acids Ex. Deoxyribose Nucleic Acid (DNA) Ribonucleic Acid (RNA)
Nucleic Acid Structure & Conformation - Intro M.Bansal.
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Nucleic Acid Structure & Conformation - Intro
M.Bansal
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--Lehninger 5th Ed
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WC base-pairing
Hoogsteen base-pairing
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The x-ray fibre diffraction pattern of sodium salt of DNA-B at 90% R.H.(Rosalind Franklin 1953)
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DNA facts:
Deoxyribose - Nucleic Acid
Base composition:
Erwin Chargaff
(A)=(T), (G)=(C)
X-ray pattern:
Rosalind Franklin
Structure:
James Watson & Francis Crick
- base pairing between
A-T and G-C
- double helical model with
10 units per turn.
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O3’-P-O5’-C5’ (g-)
P-O5’-C5’-C4’ (t)
O5’-C5’-C4’-C3’ (g+ )C5’-C4’-C3’-O3’ (2E)
C4’-C3’-O3’-P (t)
C3’-O3’-P-O5’ (g-)
Backbone conformationBackbone conformation
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The puckering of the ribose ring is described by the phase angle P, where
(ν2+ν4)-(ν1+ν3)
P = arctan -------------------------------- 2ν0[sin(π/5)+sin(2π/5)]
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B A Z
5’
5’
5’
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Torsion angle
A-DNA B-DNA Z-DNA (dinucleotide repeat)
pG pC
α -50 -46 47g+ -137 t
β 172 136 179 -140
γ 40 38 -165 56
δ 80 139 99 C3’endo 138 C2’ endo
ε -146 -133 -104 -94
ζ -45 -157 -69 g- 80 g+
χ -154 -102 68 (syn) -159 (anti)
Torsion Angles Corresponding to A, B, Z DNA Structures
n 11 10 -6 h 2.56 3.3 7.2
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The various forms of DNA have been identified as A, B, C etc.
In fact, a detailed inspection of the literature reveals that only
the letters F, Q, U, V and Y are now available, to describe any
new DNA structure that may appear in future. It is also
apparent that it may be more relevant to talk about the A, B or
C type dinucleotide steps, since several recent structures
show mixtures of various different geometries and a careful
analysis is essential before identifying it as a ‘new structure’.
A Glossary of DNA structures from A to Z A. Ghosh & M. Bansal , Acta Cryst D, vol 59 (Apr 2003)
DNA structures from A to Z