ISBN-13: 9783639070170 / Angielski / Miękka / 2009 / 84 str.
We obtained the first experimental measurements ofthe length of thedenaturation bubble appearing in the DNA meltingtransition. This isachieved by working with short oligomers which canform only one bubbleper molecule. Using a quenching technique to trap thebubble states, wecould measure the length of the bubble and therelative weights of thebubble states as a function of temperature. We foundthat the averagebubble size grows for increasing temperature, butreaches a plateau at alength of order B (the length of the AT region).After the plateau, theaverage bubble length jumps to 1. This jump of theorder parameter is asignature of a discontinuous transition, one wherethe bubble size remainsfinite up to critical temperature of strandseparation. For abubble flanked by double-stranded regions, thenucleation size is around 3bases. For bubbles opening at the ends of themolecule there is nonucleation threshold. For the first time we showexperimentally that asingle mismatch transforms a transition with manyintermediates into anearly two-state transition for oligomer length inthe range of 20 to 40bases.