20-04-2013, 03:12 PM
DNA CHIP TECHNOLOGY: A REVIEW
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ABSTRACT
The abstract describes principle used the development and design of DNA chip technology. DNA chip operating principles based on integrated circuits technology is explained in detailed. Steps involved in DNA chip design such as Probe creation, DNA chip fabrication, sample preparation and hybridization assay, readout and data analysis, two-channel vs. one-channel detection are reviewed. Applications of DNA chip technology in genomic DNA arrays in studies of gene experession and pathogens, host gene expression, comparative genomic hybridization, SNP detection, gene expression profiling, cancer research are described. At last websites ot the organizations working in the field of DNA chip technology are also given in the presented review.
Introduction
Biochips are similar to semiconductors, except that instead of having electronic circuits, they have biological material, DNA or RNA or protein, attached to the surface of a "chip," which can be glass, plastic or silicon. There are two main types of biochips, depending on the material attached. Nucleic acids are biochips, which have DNA or RNA, and protein biochips. Deoxyribonucleic acid, DNA, contains all the necessary instructions for all living organisms, except a few viruses, which are RNA based. DNA is double-stranded, and contains a nucleoside base (adenine, cytosine, guanine or thymine), a ribose sugar and a phosphate group. James Watson and Francis Crick, in 1953, discovered that the DNA was arranged in tightly twisted into double helix. DNA is grouped together as genes, although the grouping may not be directly adjacent.
DNA (genes) are differentially expressed, meaning that most of the time the majority of the DNA is silent, or unexpressed, by being tightly twisted together. But when a particular section of DNA is needed, it is expressed, or unwound so that the DNA can be read and the appropriate proteins made. This is done by copying the DNA’s instructions to RNA, specifically messenger RNA (mRNA). This process is called transcription. The mRNA then translates the DNA "message" into protein.
DNA chip operating principles
Integrated circuits technology: An integrated circuit (IC) called a chip or microchip in electronic technology is an electronic circuit built on a semiconductor substrate, usually one of a single crystal of silicon. The circuit is packaged in a hermetically sealed case or a non hermetic plastic capsule, with leads extending from it for input, output and power-supply connections, and for other connections that may be necessary when the device is put to use. There is also a different scale of integration of such circuits. In the case of very large-scale integration, an IC can contain more than 1000 transistors. Intel founder Gordon Moore observed that the number of transistors per semiconductor chip about doubles every 18-24 months. The present microprocessor chips (used in personal computers) contain more than 100 million transistors per several square centimeters. Such huge integration scale, which has almost reached manufacturing technology limits, helps to make modern computers very fast, compact and relatively inexpensive.
A comparable phenomenon is observed in molecular biology. The miniaturization of certain tools is suitable for the construction of a smart and portable device - the spotted array system, which offers the pharmaceutical, biotechnology and agriculture industries more efficient and economical solutions. DNA micro arrays built using photolithography have been on a similar pathway as integrated circuits.
Applications of DNA Chip Technology:
Some of the important applications of DNA chip technology are described below. a) Application of genomic DNA arrays in studies of gene experession and pathogens: Traditionally many of the standard methods for looking at characteristics of pathogennic organisms, such as typing of isolates, resistance to drugs and the identification of virulence, were performed on laboratory cultures. Often the scope of such tests is limited by the slow growth and fastidiousness of the organism. As a result, it can be difficult to provide information about phenotypes fast enough to be clinically relevant. In addition this information does not reveal anything about the mechanisms behind particular characteristics. Many molecular tests used in microbiological diagnostics rely on DNA sequencing or nucleic acid hybridization to identify specific sequences or point mutations that vary between different clones16- 19. An array format expands on these methods by enabling the simultaneous detection of thousands of genomic targets. This will result in more accurate and efficient genotyping plus information on the expression of specific phenotypic characteristics, such as drug resistance.