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York University
BIOL 3110
Peter Cheung

Sept 17, 2009 Factors That Promote Z-DNA Formation 1) Sequence of alternating pyrimidines & purines on the same strand 2) High salt concentrations, because the proximity of the phosphate groups in the helix are close together (creating a negative repulsion) therefore the salt helps to neutralize this repulsion. 3) Cytosine methylation makes for easier Z-DNA formation so that the genes cannot be expressed. 4) Negative super-coiling Size of DNA -The size of a DNA molecule is measured in the number of base pairs (bp), one nucleotide residue has an average molecular weight of about 330, and therefore, one base pair will weigh in at 660. -Since the average length of a nucleotide residue is about 0.34nm then the length of a kbp is approximately 340nm (refer to tab. 1.3 Signer & Burk) -The haploid length of an average mammalian chromosome is approximately 3 billion bps and with an average length of 0.34nm per bp therefore the total length is around 1m in length. DNA Bending -The idea that B-DNA is the perfect model for a normal helix is not exactly true. -The bending of the molecule itself occurs most frequently in long stretches of A’s. The pro
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