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dna chip - Tissue B(cancerous DNA chip technology permits...

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Unformatted text preview: Tissue B (cancerous) DNA chip technology permits an investigator to rapidly determine which genes are expressed by a cell or tissue. To understand how a DNA chip works, let's consider an experiment in which we want to compare the genes that are expressed in normal tissue {A} and cancerous tissue [E]. Tissue A Tlssue B [normal] (cancerous) @Efi mRNA is removed After the RNA is removed. investigators can use a DNA chip to compare the two cDNA samples. A DNA chip can contain an array of 60,000 or more different DNA sequences. called probes. The probes are single-stranded and typically 20 nucleotides long. Each represents a tiny but unique region of a gene in the genome A scanner detects patterns of hybridization by sensing the fluorescent signals. In this examPle. a green spot indicates cDNAs from the cancerous tissueA red spot indicates binding of cDNAs from normal tissue.A yellow spot indicates that cDNAs from both tissues bind to the DNA in that area of the chip. fissue B {cancerous} When a gene is expressed, it is transcribed into mRNA (green). 111 this experiment. the mRNAs from the two tissues are isolated and converted into complementary strands of DNA [cDNAs) by the enzyme reverse transcriptase. To distinguish between the two pools of cDNAs. they are fluorescently labeled [hunted and green). "'""'- (DNA from cancerous nucleotide sequence In probe: ATI'I'I'AGGAACAAAGG'I'I'I'I’ sequence in probe: GGGCCATAGGCCI'CGGCI'GG The cDNA samples are mixed together and added to the chip cDNAs that are complementary to the probes on the chip will bind [hybridize] with the DNAi and thereby stick to that location on the chip. Unbound cDNAs are washed away. hybridization to cDNA from cancerous hybridization to cDNA from no hybridize! CD Because each area of the chip contains a known DNA sequence. corresponding to a known gene. the identities of the hybridizing cDNAs can be determined. Using this data. investigators can establish which genes are expressed differently in the cancerous tissue, and thus may be able to design better treatment strategies. ...
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