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A-DNA and Z-DNA Atlases. Dave Ussery Comparative Microbial Genomics first lecture, 18 September, 2002. Outline. Helix family. A-DNA. A-DNA helix. A-DNA was the first DNA helix characterised by Rosalind Franklin in the early 1950’s. A-DNA helices
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A-DNA and Z-DNA Atlases Dave Ussery Comparative Microbial Genomics first lecture, 18 September, 2002
A-DNA A-DNA helix A-DNA was the first DNA helix characterised by Rosalind Franklin in the early 1950’s. 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.
B-DNA B-DNA helix 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.
Z-DNA Z-DNA helix 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.
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?
