Research About Effect Of Fluoride Ion On The Stability Of DNA Hairpin Via Single Molecular Manipulation Of Magnetic Tweezers

In this thesis,we do some research about effect of fluoride ion on the stability of DNA hairpin and the properties of sodium polystyrenesulfonate by magnetic tweezers.Magnetic tweezers are a versatile single-molecule technique that permits the application of both forces and torques to biological macromolecules and their complexes.The various implementations of Magnetic Tweezers are all based on attaching micrometer-sized superparamagnetic beads or particles to the biological assembly of interest.The superparamagnetic particles,in turn,can be manipulated by magnetic fields that are generated by permanent or electromagnets.As a mature single molecular technology,magnetic tweezers have the properties of wonderful stability?no heating or lighting damage to samples?long time for measuring and concise setup.So far there are some examples of modified function adding to magnetic tweezers,and more upgrade will be made on magnetic tweezers for its concise setup.About the former:Fluoride prevents tooth decay as an additive in tooth paste and other oral hygiene products,while high dose intake of fluoride from contaminated drinking water leads to fluorosis.There were some research about fluoride focusing on the region of biochemistry before this work,here we studied the effect of fluoride ion on the stability of DNA double helix using sensitive single molecule manipulation technique of magnetic tweezers.Hairpin occurs when two regions of the same strand,usually complementary in nucleotide sequence when read in opposite directions,base-pair to form a double helix that ends in an unpaired loop.The force of the cross point at which the open rate equals to the close rate is defined as critical force,and the equilibrium critical force decreases with increasing concentration of fluoride ion.The stability of DNA double helix decreases by 0.05 kBT per base pair with fluoride ions concentration of 1 mM,and 0.1 kBT per base pair with fluoride ions concentration of 100 mM.Our results give the first quantitative measurement of DNA stability in the presence of fluoride ions,which might disturb DNA-related biological processes to cause fluorosis.DNA is polymer and polyelectrolyte,so magnetic tweezers can be used to study other polyelectrolytes.For the latter:As a polymer of strong polyelectrolyte,similar to DNA,the elasticity of sodium polystyrenesulfonate can also be researched by magnetic tweezers.