Medida da elasticidade entrópica de uma molécula de DNA

Abstract

In this work we combine optical tweezer and videomicroscopy techniques to obtain the entropic elastic behavior of single ¸ phage DNA molecules. By tethering a single DNA molecule by one end to a 3¹m poliestirene bead and by the other end to a microslide, we build a microscopic analog of an over-damped mass{spring system, that can be stretched using the optical tweezer. When the tweezer is turned o®, the DNA recoil can be followed through the recoil of the tethered bead. The motion of the bead is videorecorded and the images are digitized for posterior analysis. The force that the stretched DNA exerts on the bead is well described by the wormlike chain (WLC) model for °exible polymers. Persistence lengths for single pure DNA molecules and for DNA + ethidium bromide complexes are obtained.