Sequencing Chemistries

The goal of DNA sequencing is to obtain information about the sequence of nucleotide bases—adenine (A), guanine (G), cytosine (C), and thymine (T)—which constitutes a particular DNA molecule. In order to obtain this information, the sample under investigation is modified in DNA sequencing reactions, which can be based on one of two approaches: enzymatic synthesis of DNA fragments with chain termination by dideoxynu-cleotides ddNTP (terminators)[1] or by chemical degradation method.[2] The first method is faster, easier to implement, and it is currently the method of choice. Terminators (ddNTP) lack a 3'OH group that is necessary for the extension of DNA's sugar phosphate backbone. Thus the DNA chain cannot be extended beyond the incorporated ddNTP. A mixture of all four dNTPs and one ddNTP is used in each reaction. For example, in a T-terminated reaction a ddTTP is added to a mixture of dNTPs. This allows elongation of the DNA chain until ddTTP is occasionally attached to the growing molecule, which stops the reaction. This process is random and as a result, fragments of different lengths are produced, each terminated at a T-position, for all T's from the primer to the end of the sequence. Four reactions are required for complete description of the DNA sequence, each representing an A-, C-, G-, or T-terminated ladder. In order to enable observation of DNA bands, the fragments are labeled with a tag (radioactive or fluorescent) attached to either the primer (primer chemistry) or ddNTPs (terminator chemistry).

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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