ADNA and ZDNA Atlases

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A-DNA and Z-DNA Atlases

Dave Ussery Comparative Microbial
Genomics first lecture, 18 September, 2002
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Outline
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Helix family
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A-DNA helix
A-DNA
A-DNA was the first DNA helix characterised by
Rosalind Franklin in the early 1950s. A-DNA
helices tend to be favoured by stretches of
purines (or pyrimidines) of at least 4 bp. A-DNA
helices are found in RNA-DNA hybrids.
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B-DNA helix
B-DNA
B-DNA is the classic helix described by Watson
and Crick in 1953. It has, on average, about 10
bp/turn of the helix and is the AVERAGE structure
for many DNA sequences.
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Z-DNA helix
Z-DNA
Z-DNA was the first DNA helix to be crystallised
(in 1979), and came to the surprise of many
biologists. It is a thin, LEFT-HANDED helix,
with 12 bp/turn, and has a zig-zag backbone
(hence its name). Certain alternating
pyrimidine/purine sequences (e.g., CGCGCG) will
form this helix.
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How Random is DNA?
Consider a stretch of purines (G or A,
abbreviated R) of length n What is the
probability of finding this in a random DNA
sequence?
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Ecoli
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C.jejuni
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S.cerevisiae
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H.sapiens
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All Organisms
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Archaea
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Proteobacteria
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Tom Cavilier Smith
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Firmicutes
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Other Bacteria
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Proctista
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Protozoa
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Leishmania major 1
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Lmajor 1 genome
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Lmajor 1 ADNA
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Lmajor 1 ZDNA
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Lmajor 4 genome
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Lmajor 4 ADNA
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Lmajor 4 ZDNA
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P.falciparium 2 genome
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P.fal 2 ADNA
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P.fal 2 ZDNA
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coding vs. noncoding
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coding vs. noncoding