procedures still provide valuable information for the diagnosis and control of infectious diseases.
Enzymatic digestion of DNA is accomplished using any of a number of enzymes known as restriction endonucleases. Each specific endonuclease rec ognizes a specific nucleotide sequence (usually four to eight nucleotides in length) known as the enzyme's recognition, or restriction, site. Once the recognition site is located, the enzyme catalyzes the digestion of the nucleic acid strand at that site,
Figure 8-14 Overview of high-density DNA probes. High-density oligonucleotide arrays are created using light-directed chemical synthesis that combines photolithography and solid-phase chemical synthesis. Because of this sophisticated process, more than 500 to as many as a million different oligonucleotide probes may be formed on a chip; an array is shown in A. Nucleic acid is extracted from a sample and then hybridized within seconds to the probe array in a GeneChip Fluidics Station. The hybridized array (B) is scanned using a laser confocal fluorescent microscope that looks at each site (i.e., probe) on the chip and the intensity of hybridization is analyzed using imaging processing software. The Affymetrix system is shown in part C. From left to right is the GeneChip Fluidics Station, scanner, and computer system for data. (Courtesy Affymetrix, Santa Clara, Calif.)
Nucleic acid obtained by extracting chromosomal or plasmid DNA from bacterial culture, or by PCR amplification of target nucleic acid
Restriction enzymatic digestion by endonuclease
Example: EcoR 1 endonuclease digestion cut
Gel electrophoresis to separate DNA digestion fragments
Restriction ' pattern
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