Microarrays: Definition & Analyzing Genes on a Chip

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  • 0:03 What Are Microarrays?
  • 0:37 Types of Microarrays
  • 1:20 How Microarrays Analyze Genes
  • 3:11 Why Do We Use DNA Microarrays?
  • 4:16 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

DNA microarrays are used to quickly and efficiently measure the gene expression levels of many genes at the same time. In this lesson, you will learn how microarrays are produced and used by scientists to help identify and treat diseases.

What are Microarrays?

Microarrays are used to conduct many tests on biological material like DNA very quickly and without using up much material. Microarrays can be used to detect proteins, DNA, RNA, antibodies, carbohydrates, or other chemical compounds, although DNA microarrays are the most commonly used today. Microarrays have revolutionized DNA analysis, allowing the expression levels of many genes to be measured at the same time.

Types of Microarrays

There are two main types of microarrays available today. The first is called a solid phase array and it is made by putting tiny spots of DNA onto a glass, plastic or silicon plate. These tiny DNA fragments are called probes and they will be used to bind to specific DNA sequences in the test sample. Hundreds or even thousands of short segments of DNA can be placed by robotic machines onto a single array. In a similar process, polystyrene bead arrays put DNA probes onto tiny plastic beads that can be mixed with a test sample of DNA.

How are Microarrays Used to Analyze Genes?

Although your body contains the exact same DNA in every cell, not all of the genes are active at the same time in every cell. DNA microarrays tell us which genes are being expressed and are active in a particular cell. Scientists use DNA microarrays to determine which genes are active both when cells are functioning normally and to find out when certain genes are not functioning correctly. When a gene is activated, it is copied onto messenger RNA (mRNA). So, to determine which genes are active in a cell, you need to collect all the mRNA in the cell. Once the mRNA is collected, a researcher will add an enzyme to it that will make DNA copies of each mRNA strand.

Fluorescent markers will also be added to each DNA strand. The sample of DNA will then be placed onto the microarray, which is pre-loaded with probe DNA.

DNA in the test sample that is complementary to the probe will bind to it strongly, and DNA that is different will not bind. This process of DNA binding to complementary DNA is called hybridization. After giving the test DNA time to hybridize, the solution is washed off so that only DNA that is strongly bound to the probe will remain. The array is placed onto a detector that can see the fluorescent markers that were added to the test DNA. The strength of the fluorescent signal detected corresponds to the amount of test DNA that hybridized to the probe. This can then be compared to a standard to determine the expression level of a gene.

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