Chain Termination Method

Because it employs fewer steps and does not require the use of restriction enzymes, the chain termination method of DNA sequencing is used in more laboratories than is the Maxam-Gilbert approach. Chain termination sequencing is a clever variation of the reaction used to replicate DNA, and requires only a handful of components. Four reaction tubes, designated "A," "C," "G," and "T," are prepared and the DNA strand whose sequence is to be determined is added into each tube. This DNA strand is called the template.

Along with the template, a short, single-stranded piece of DNA (called a primer) is added; it attaches specifically to one section of the template and serves as a starting point for synthesis of a new DNA strand. Also added are the four "building block" nucleotides, a buffer (to maintain the proper pH level), the enzyme DNA polymerase, and its cofactor magnesium, all of which are needed to extend the primer into a full-length DNA chain.

restriction enzymes enzymes that cut DNA at a particular sequence buffers substances that counteract rapid or wide pH changes in a solution

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