Lecture11_NABPty2012 (1)

J r huth et al nature struct biol 4 657 1997 2ezepdb

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Unformatted text preview: high temperatures If the temperature is lowered, the strands recombine. The rate of recombination is inversely proportional to the complexity of the DNA. 100 80 % Denatured The temperature at which this “denaturation” or “melting” occurs (tm) depends on the pH and salt concentration, and increases approximately linearly with the GC content of the DNA. 60 40 20 0 70 40 40 50 60% GC 30 50 60 70% GC 80 90 100 o Temperature / C 110 Double-stranded and single-stranded DNA differ in their optical absorption at 260 nm dA dG dU dC The conjugated π-electron systems of the purine & pyrimidine bases absorb strongly in the UV. nucleotides ssDNA dsDNA The The absorbance of double-stranded DNA (dsDNA) at 260 nm is less than that of either single-stranded DNA (ssDNA) or the free bases. This is called “hypochromism.” Hypochromism results from dipole-dipole interactions between neighboring bases The excited states of an interacting pair of molecules can be described as linear The combinations of the excited states of the individual molecules. In certain geometries, some of the absorption strength in the near-UV moves to bands at higher energies. increasing energy empty orbitals strong absorption band light filled orbitals individual base strong band near 2...
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This note was uploaded on 02/17/2012 for the course CHEM 212 taught by Professor Staff during the Fall '10 term at Rutgers.

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