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Cells and Gene Expressions
It is true that human genome contains more than 30,000 genes. It is also true that every cell of the human body contains the same genome, but not all genes are expressed in every cell. Some specific genes are turned on and expressed when needed. For example, in liver cells, genes are expressed for enzymes that detoxify poisons, similarly, in pancreas; genes are expressed for producing insulin.
Gene expression, therefore, is defined as the transcription of the information retained inside the DNA molecule, the storehouse of genetic information into mRNA that translates into proteins and performs the most crucial functions of cells. Scientists are interested in knowing how cells achieve such perfection by analyzing the types of mRNA produced by a cell to find out which specific genes are expressed, which in turn provides insights into how the cell responds to its changing needs. Scientists conducting genetic studies using microarray technique have developed a tool called DNA microarray that allows them to scrutinize many genes at a time and help determine which gene is expressed in a specific cell and at a specific point of time.
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DNA Microarray Technology
A microarray technology works by utilizing the capability of a given mRNA to bind particularly to, or hybridize to the same DNA template from where it originated. The technology uses an array that contains several DNA samples. Scientists can find out the expression levels of thousands of genes within a cell by computing the amount of mRNA attached to each site on the array. Using a computer, the amount of mRNA attached to the spots on the microarray is accurately measured, generating a profile of gene expression in the cell.
Mechanism of a DNA Microarray Experiment:
- Isolation of mRNA from cell cultures
- Reverse transcribe mRNA into cDNA using a reverse transcriptase enzyme
- Label cDNA using florescently labeled nucleotides
- Hybridize labeled cDNA with nucleic acid probes present in the array
- Wash off unhybridized cDNA and scan with laser scanner
- Analyze data using a computer
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Importance of Microarray Technology
Microarrays are significant because they possess a huge number of genes and also because of their portable size. Microarrays are therefore, helpful when one is interested in surveying a large number of genes swiftly or when the sample of interest is small. Microarrays can also be helpful to assay gene expression within each sample or to compare gene expressions of two different cell types or tissue samples, for example, healthy and diseased tissue. Microarray is being used to detect the gene expressions in prostrate cancer, oral cancer, breast cancer, ovarian caner, and other types of cancers. Since a microarray technology has the potential to examine the expression of several genes at a time, it promises to revolutionize the way scientists study gene expression.
Applications of DNA Microarray Technology:
- Disease diagnosis
- Drug discovery i.e., Pharmacogenomics
- Toxicological Research i.e.,Toxicogenomics
- Immunology: study of host genomic responses to bacterial infections
Advantages of Microarray Technology
- The technology allows the study of several genes at a time
- The high speed is one of the main benefits of this technology.
- The technology is relatively cheaper to use
- It is user-friendly
- It is both adaptable and comprehensive
Limitations of Microarray Technology
- Involves a number of steps including chip production, probe hybridization, image quantification, normalization, and data interpretation
- Analysis of large statistical data
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(Web): DNA Microarray (Genome Chip) --- Monitoring the Genome on a Chip -- http://www.gene-chips.com/
(Web): MICROARRAYS: CHIPPING AWAY AT THE MYSTERIES OF SCIENCE AND MEDICINE -- http://www.ncbi.nlm.nih.gov/About/primer/microarrays.html#microarrays