Question

What are gene microarrays? How are microarrays used?

Short answer

Answer: The purpose of using a gene microarray in studying gene expression is to simultaneously measure the expression levels of thousands of genes, allowing researchers to identify differences in gene expression patterns across various tissues or conditions. This can help in understanding gene function, the molecular basis of diseases, and in developing new therapies for various medical conditions.

Step-by-step solution

Introduction to Gene Expression

Gene expression is the process by which the information stored in a gene is used to produce a functional product, such as a protein. This occurs in two main steps: transcription, where the DNA sequence of the gene is copied into an RNA molecule, and translation, where the RNA molecule is used to create a protein. The level of gene expression can vary between different tissues or in response to different conditions, and understanding these differences can provide insights into the functions of genes and the molecular basis of diseases.

What are Gene Microarrays?

A gene microarray, also known as a DNA microarray or DNA chip, is a high-throughput technology used to measure gene expression levels simultaneously across thousands of genes. A microarray consists of a solid support, such as a glass slide or silicon chip, onto which DNA fragments representing individual genes are immobilized in a grid-like pattern. Each spot on the array contains thousands to millions of identical DNA molecules, called probes, that can specifically hybridize, or bind, to a complementary RNA molecule from the sample being analyzed.

Preparation of Microarrays

The first step in creating a microarray is designing the probes. Researchers choose a set of genes they are interested in studying and obtain the DNA sequence for each gene. Then, they synthesize short fragments of DNA (usually about 25-60 base pairs long) that are complementary to a specific region of each gene's RNA transcript. These fragments are then chemically attached to the surface of a solid support, such as a glass slide, in a precise pattern to create the microarray.

Sample Preparation and Hybridization

To use a microarray to analyze gene expression in a sample, researchers first isolate the total RNA from cells or tissues of interest. The RNA is then reverse transcribed to create a complementary DNA (cDNA) copy. This cDNA is labeled with a fluorescent dye, usually green or red, such that it can be visualized using a specialized scanner. The labeled cDNA is then hybridized, or allowed to bind, to the probes on the microarray. Since the probes are designed to specifically bind to their complementary RNA sequences, the amount of cDNA bound to each spot on the array reflects the level of expression of the corresponding gene in the sample.

Data Collection and Analysis

After hybridization, the microarray is scanned using a specialized scanner that detects the fluorescent signal from each spot. The intensity of the fluorescence is directly proportional to the amount of cDNA bound to each probe, and therefore, to the level of gene expression. The data collected from the microarray can then be analyzed using various statistical and bioinformatics tools to identify patterns of gene expression and to compare them across multiple samples or conditions. This can help researchers uncover important information about gene function, the molecular basis of diseases, and the development of new therapies for various medical conditions.