Condensation transition in DNA-polyaminoamide dendrimer fibers studied using optical tweezers.
When mixed together, DNA and polyaminoamide dendrimers form fibers that condense into a compact structure. We use optical tweezers to pull condensed fibers and investigate the decondensation transition by measuring force-extension curves (FECs). A characteristic force plateau (around 10 pN) and hysteresis between the pulling and relaxation cycles are observed for different dendrimer sizes, indicating the existence of a first-order transition between two phases (condensed and extended) of the fiber. Upon salt variation FECs change noticeably confirming that electrostatic forces drive the condensation transition. We propose a simple model for the decondensing transition that qualitatively reproduces the FECs and which is confirmed by atomic force microscopy images.
Ritort
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Department of Physics and Molecular & Cell Biology, University of California, Berkeley, California 94720, USA.
Mihardja
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Smith
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Bustamante
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D010582:Bacteriophage lambda / Q000737:chemistry; D003198:Computer Simulation; D004279:DNA, Viral / Q000737:chemistry*; D050091:Dendrimers / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008956:Models, Chemical; D044367:Phase Transition; D011073:Polyamines / Q000737:chemistry*
D004279:DNA, Viral; D050091:Dendrimers; C104700:PAMAM Starburst; D011073:Polyamines