DNA微阵列

• 脱氧核糖核酸microarrays are solid supports, usually of glass or silicon, upon which DNA is attached in an organized pre-determined grid fashion.
• DNA的每个斑点（称为探针）代表一个基因。
• 脱氧核糖核酸microarrays can analyze the expression of tens of thousands of genes simultaneously.
• There are several synonyms of DNA microarrays such as DNA chips, gene chips, DNA arrays, gene arrays, and biochips.

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Principle of DNA Microarray Technique

• The principle of DNA microarrays lies on the hybridization between thenucleic acidstrands.
• The property of complementary nucleic acid sequences is to specifically pair with each other by forming hydrogen bonds between complementary nucleotide base pairs.
• For this, samples are labeled using fluorescent dyes.
• 至少将两个样品杂交与芯片杂交。
• 样品与附着在芯片上的探针之间的互补核酸序列通过氢键配对。
• The non-specific bonding sequences while remain unattached and washed out during the washing step of the process.
• 与探针序列结合的荧光标记的目标序列会产生信号。
• The signal depends on the hybridization conditions (ex: temperature), washing after hybridization etc while the total strength of the signal, depends upon the amount of target sample present.
• Using this technology the presence of one genomic or cDNA sequence in 1,00,000 or more sequences can be screened in a single hybridization.

DNA微阵列的类型

There are 2 types of DNA Chips/Microarrays:

1. cDNA based microarray
2. Oligonucleotide based microarray

Spotted DNA arrays (“cDNA arrays”)

• Chips are prepared by using cDNA.
• Called cDNA chips or cDNA microarray or probe DNA.
• The cDNAs are amplified by using PCR.
• 然后将它们固定在由载玻片（1 x 3英寸）的尼龙丝（1 x 3英寸）组成的固体支架上。通过毛细管作用将探针DNA加载到斑点旋转中。
• Small volume of this DNA preparation is spotted on solid surface making physical contact between these two.
• 脱氧核糖核酸is delivered mechanically or in a robotic manner.

Oligonucleotide arrays (Gene Chips)

• 在寡核苷酸微阵列中，将短DNA寡核苷酸发现在阵列上。
• Small number of 20-25mers/gene.
• The main feature of oligonucleotide microarray is that each gene is normally represented by more than one probe.
• Enabled by photolithography from the computer industry
• 现成的

Requirementsof DNA Microarray Technique

设计DNA微阵列系统的某些要求，即：

1. 脱氧核糖核酸Chip
2. Target sample (Fluorescently labelled)
3. 荧光染料
4. Probes
5. 扫描器

涉及基于cDNA的微阵列的步骤

The reaction procedure of DNA microarray takes places in several steps:

1. 样品的收集

• 样品可能是一个有机体th细胞/组织at we wish to conduct the study on.
• Two types of samples are collected: healthy cells and infected cells, for comparison and to obtain the results.

2. mRNA的分离

• RNA is extracted from the sample using a column or solvent like phenol-chloroform.
• From the extracted RNA, mRNA is separated leaving behind rRNA and tRNA.
• 由于mRNA具有聚-A尾部，因此使用带有聚-T尾的柱珠来结合mRNA。
• 提取后，将色谱柱用缓冲液冲洗以将mRNA与珠子分离。

3. Creation of labeled cDNA

• To create cDNA (complementary DNA strand), reverse transcription of the mRNA is done.
• 然后将两个样品与不同的荧光染料合并，以产生荧光cDNA链。这有助于区分cDNA的样品类别。

4. Hybridization

• The labeled cDNAs from both the samples are placed in the DNA microarray so that each cDNA gets hybridized to its complementary strand; they are also thoroughly washed to remove unbounded sequences.

5. 收集和分析

• The collection of data is done by using a microarray scanner.
• 该扫描仪由激光，计算机和相机组成。激光激发了cDNA的荧光，产生信号。
• 当激光扫描阵列时，相机记录了产生的图像。
• Then the computer stores the data and provides the results immediately. The data thus produced are then analyzed.
• The difference in the intensity of the colors for each spot determines the character of the gene in that particular spot.

Applications of DNA Microarray

• In humans, they can be used to determine how particular diseases affect the pattern of gene expression (the expression profile) in various tissues, or the identity (from the expression profile) of the infecting organism. Thus, in clinical medicine alone, DNA microarrays have huge potential for diagnosis.

此外，它在许多领域中都有申请，例如：

• 发现药物
• Diagnostics and genetic engineering
• Alternative splicing detection
• 蛋白质组学
• 功能基因组学
• DNA测序
• 基因表达分析
• 毒理学研究（毒理学学）

Advantages of DNA Microarray

• Provides data for thousands of genes in real time.
• Single experiment generates many results easily.
• Fast and easy to obtain results.
• Promising for discovering cures to diseases and cancer.
• DNA的不同部分可用于研究基因表达。

Disadvantages of DNA Microarray

• Expensive to create.
• 一次产生过多的结果需要很长时间进行分析，这本质上很复杂。
• The DNA chips do not have very long shelf life.

参考

1. https://www.slideshare.net/Haddies/dna-microarray-dna-chips
2. https://www.slideshare.net/mahendrareddy59/dna-microarray-56074935
3. https://www.news-medical.net/life-sciences/dna-microarray.aspx
4. https://www.researchgate.net/figure/steps-in-dna-microarray-experiment-iii-gene-gene-expression-data-a-a- typical-typical-dna-tna-microarray_fig1_23686868392
5. https://bitesizebio.com/7206/introduction-to-dna-microars/
6. http://www.highveld.com/molecular-biology/oligonucleotide-microarrays.html
7. https://courses.cs.washington.edu/courses/cse527/04au/slides/clect02.pdf

DNA微阵列