title: Condensation transition in DNA-polyaminoamide dendrimer fibers studied using optical tweezers.
abstract: 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.
authors.affiliation: Department of Physics and Molecular & Cell Biology, University of California, Berkeley, California 94720, USA.
authors.forename: F
authors.initials: F
authors.lastname: Ritort
authors.forename: S
authors.initials: S
authors.lastname: Mihardja
authors.forename: S B
authors.initials: SB
authors.lastname: Smith
authors.forename: C
authors.initials: C
authors.lastname: Bustamante
mesh_terms: 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*
chemical_list: D004279:DNA, Viral; D050091:Dendrimers; C104700:PAMAM Starburst; D011073:Polyamines