Overview

DNA hybridization methods exploit the base-pairing properties that enable one strand of DNA to recognize its specific complementary strand to form the double-stranded DNA molecule. Thus on a microarray chip, a single strand of DNA tethered to a surface (a probe) can readily hybridize with its single-stranded complement even in a complex mixture of many other DNA molecules. When the target molecules are fluorescently labeled, the resulting signal at a particular location on the array establishes the existence of the complimentary sequence in the target.

Polymerase chain reaction (PCR) is another technology where DNA hybridization plays a central role. In PCR, the initial hybridization is between the oligonucle-otide primers and the target DNA to be amplified. The PCR reaction produces large numbers of copies of a defined DNA fragment. The primers bind to a complementary sequence and initiate extension of the adjacent DNA regions using DNA polymerase. Primer design is one of the key determinants for the specificity and the yield of the reaction. Robust PCR primer design requires that the melting temperatures of the two primers must be closely matched.

Thus the melting temperature is one of the primary design variables in both of these technologies. The melting temperature, Tm, of a DNA duplex is defined as the temperature where one-half of the nucleotides are paired with their complement and one-half are unpaired. Tm is typically measured as the midpoint of the spectroscopic hyperchromic absorbance shift during DNA melting. Tm depends mainly on the DNA GC base content, cation concentration of the buffer, and DNA double-strand length. Currently, the most accurate prediction of Tm for oligonucleotide DNA uses the thermo-dynamic nearest-neighbor (NN) model. The NN model for nucleic acids assumes that the stability of a given base pair depends on the identity and orientation of neighboring base pairs. The NN model basic assumption is that probe free energy can be calculated from the enthalpy and entropy of all NN pairs. NN calculations for Tm prediction are useful for microarray design and for the selection of PCR primers and hybridization probes.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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