![]() Next the intensity of each hybridization signal is translated into a table with numerical measures. mRNA molecule can hybridize to a melted cDNA molecule when the mRNA contains the complementary code of the cDNA strands) of the target to the probes determines a chemical reaction that is captured into a digital image by a scanning laser device. Hybridization (process of base pairing two single strands of DNA or RNA viz. Strands of cDNA (target) in the pool hybridize to complementary sequences (probe) on the array and any unhybridized cDNA (target) is washed off. Two pools of differentially labeled cDNA (or target) are combined and applied to a microarray. mRNA => cDNA) into cDNA and labeled with one of two fluorescent dyes, "red" and "green". Next, pools of purified mRNA from cell populations under study are reverse-transcribed (synthesis of a complementary DNA strand from RNA molecule viz. ESTs are the probes that represent either genes of known identity or segments of functional DNA. In the first step, samples of DNA clones (or probes) with known sequence content are spotted and immobilized onto a glass slide or other substrate called "microarray" so that each spot in the microarray corresponds to a gene or an EST (expressed sequence tag). DNA fragments can be derived from cDNA or short synthesized oligonucleotides. Microarrays consist of a high-density array of DNA fragments with a defined location fixed on a small glass surface. These are also called as DNA chips, gene chips, biochips, DNA microarrays or simply the arrays. ![]() Microarrays are the microscopic array of single-stranded DNA molecules immobilized on a solid surface by biochemical synthesis. ![]() Expression comparison of all genes in different cells of the same individual or same cells of different individuals provides an insight into the mechanism responsible for development of a certain condition or disease. Systemic analysis of data gathered in microarray gene expression measurement is performed by various bioinformatic methods such as group analysis, annotation analysis as well as network and pathway analysis. Gene expression differences in two groups of samples are discovered and quantificated by comparison of signal intensity values in microarray spots. Core principle of this method is hybridization of complementary nucleotides (A-T and G-C), which leads to creation of double stranded nucleic acids. These molecules are used for the discovery of specific RNA molecules isolated from various biological samples of interest. Microarray gene expression analysis is high-throughput method in which many different sized DNA molecules are attached to solid surface in designated spots. ![]()
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